About the author: Zhao Qingbo, born in 1950, is a professor-level senior engineer, a senior technical expert of China Petroleum and Natural Gas Corporation, and an adjunct professor of China Geo University (Wuhan); Deputy head of coalbed methane group of China Petroleum Institute; Mainly engaged in the exploration and development of coalbed methane, writing monograph 17 and publishing more than 50 academic papers. Address: Institute of Coalbed Methane, Box 44, Wanzhuang, Langfang, Hebei. Tel: (010) 69213108. E-mail:zhqib@petrochi-na.com.cn

(Langfang Branch of China Petroleum Exploration and Development Research Institute Langfang 065007)

Abstract: The reservoir-forming modes of coalbed methane can be divided into three types: autogenous, self-storage, adsorption, autogenous and self-storage, and endogenous and external storage. The reservoir-forming period of coalbed methane can be divided into early reservoir-forming period, late structural transformation period and mining period, and the conditions for reservoir-forming in mining period are pointed out in particular. The micro-cycle in thick coal seam is analyzed by sedimentary facies, and the gas-rich section of high-quality coal seam is divided into fine sections. Further use sedimentary facies to discuss the types of coal-forming parent materials and their control effect on high yield and enrichment of coalbed methane; The mechanism of tectonic stress field and hydrodynamic force on coalbed methane reservoir formation is expounded. This paper summarizes the characteristics of coalbed methane mining, points out three stages of coalbed methane well mining: blocking, unblocked and undersaturation, and thinks that the undersaturation stage can be divided into several decreasing stages. There are three types of mining characteristics: self-sufficiency, export and import. According to the geological conditions, the applicability and domestic application effects of two-dimensional seismic AVO, directional pinnate horizontal well, ultra-short radius hydraulic jet, U-well and V-well drilling technology are analyzed.

Key words: CBM reservoir-forming model, applicable technology for high-yield enrichment and coal-forming parent material mining characteristics.

Analysis on reservoir-forming conditions, production characteristics and applicable technologies of coalbed methane

Zhao Qingbo Sun Fenjin Li Wuzhong Wang Bo Sun Kong

(Petroleum Exploration and Development Research Institute of China Petroleum Langfang Branch, Langfang 065007)

Abstract: The reservoir-forming model of coalbed methane can be divided into three types: adsorbed gas autogenous reservoir, free gas autogenous reservoir and external storage autogenous source rock. The three stages of reservoir formation are early reservoir formation, late reservoir formation after structural transformation and secondary reservoir formation during development. In particular, the conditions of secondary aggregation during development are pointed out. Analysis of microcirculation in thick coal seam by sedimentary facies. The coal seams with high gas content are classified, and the types of coal-forming sources and their control effects on the production and enrichment of coalbed methane are further discussed. The mechanism of tectonic stress field and hydrodynamic force on coalbed methane accumulation is expounded. The production characteristics of coalbed methane wells are summarized: the blocking, unblocked and unsaturated production stages are pointed out, and the unsaturated stage can be divided into several depletion stages; The localization of structure and heterogeneity of inner layer lead to three production characteristics: self-operated, export-oriented and import-oriented. According to the geological background, the applicability and effect of two-dimensional seismic AVO, pinnate horizontal multilateral well, ultra-short radius hydraulic jet, U-type and V-type drilling technology are analyzed.

Keywords: coalbed methane; Accumulation mode; Coal-forming source; Productivity and richness; Production characteristics; appropriate technology

Analysis of reservoir-forming conditions of 1 coalbed methane

1. 1 coalbed methane accumulation mode and accumulation period

1. 1. 1 coalbed methane accumulation models can be divided into three categories.

Self-generation, self-storage and adsorption type: most of coalbed methane exists in coal seam in adsorption state and is enriched in slope zone with relatively stable structure. For example, the average daily gas production of horizontal wells in panzhuang in the south of Qinshui Basin is 30,000 m3; The buried depth of No.3 coal in Zhengshi 60 well1337m, and the daily gas production is 2000m3.

Self-generation and self-storage free type: coal seam adsorbed gas and free gas are relative, and most of them are homologous symbiotic interaction. Some coalbed methane exists in the coal seam in a free state, and some are mainly local structural high points. In the early stage, the coal seam was buried deeply, and the gas production was high. In the later stage, the uplifted coal seam became shallow, the compaction was weak, the secondary cleat developed and the permeability was good. The two wings are guided by hydrocarbon supply, and local high points form high-permeability and high-yield enrichment areas under favorable sealing conditions. Well Cai 504 in Cainan area of Junggar Basin has developed fault blocks, high points and good physical properties. Free gas and adsorbed gas coexist, with a coal seam depth of 2575 meters and a daily gas production of 6500m3.

Endogenous external storage type: As a source rock, the gas generated by coal seam migrates to the upper part or surrounding rock, and under favorable trap conditions, free gas reservoirs are formed in sandstone and limestone, which makes the adsorbed gas and free gas have homology, symbiosis, transformation and superposition, and can be superimposed to form a large area distribution on the plane. The roof sandstone of Shanxi Formation of Well WL2~0 15 in Hancheng area on the eastern edge of Ordos Basin is 14. 1m thick, the wellhead pressure after fracturing is 2.32MPa, and the daily gas production is 2400m3.

Figure 1 coalbed methane accumulation model diagram

1. 1.2 The accumulation period of coalbed methane can be divided into three categories.

Early reservoir formation: With the progress of sedimentation, the buried depth of coal seam gradually increases, and a large number of gases are continuously generated. Sufficient gas generating environment, good migration and accumulation potential energy, sufficient adsorption and favorable sealing conditions, high saturation and high permeability have laid the foundation for early reservoir formation. The δ 13c 1 of this kind of gas reservoir is relatively heavy (table 1), showing the characteristics of primary gas reservoirs.

Reservoir formation in the late stage of structural transformation: once the dynamic balance of the system is broken by structural fault activities, that is, the coalbed methane reservoir is opened by water and the coal seam cracks are filled by calcite veins, then the energy is readjusted, hydrocarbons are redistributed, the ancient coalbed methane reservoir is destroyed, and new high-yield and enriched blocks begin to form (Figure 2).

After being uplifted by the structure, the fault anticline structure appeared locally, which reduced the pressure of coal seam and desorbed the gas. The cracks generated by the structural movement communicated with the gas at the lower part, and made it migrate and gather to the local structural high point. When the basin sinks and receives sedimentation, the pressure gradually increases, the natural gas is regenerated, and the natural gas in the anticline wing is reabsorbed and accumulated. Most of these gas reservoirs are secondary, and δ 13C 1 is relatively light (table 1).

Table 1 CH4 content and δ 13C 1 distribution of different types of gas reservoirs

Fig. 2 Migration and accumulation process of coalbed methane.

Secondary reservoir in mining: The original state of coalbed methane is adsorption state. When the pressure drops to the critical point in mining, it breaks the original equilibrium state and becomes free state, and gas and water will be redistributed, desorbed or displaced, thus forming secondary reservoir in coalbed methane mining, which is a condition that conventional oil and gas do not have. The methane content of this kind of gas reservoir in coal mine area is low near goaf.

(1) Migration of coalbed methane in secondary reservoirs

Channeling means that gas migrates to high places or high permeability areas, and water migrates to low places, forming a three-phase flow of pulverized coal, gas and water, which enters a residual state after several years of development, producing a large number of micropores and deep gas. In the process of coalbed methane mining, some wells in the same area have high production and some wells have low production, which is related to their structural position. The desorbed gas flows or "dissociates into reservoirs" in different directions at the top of the structure or high-permeability channels, and the coalbed methane is displaced, which makes the gas at the high point less, and even flows by itself in the later stage, resulting in less syncline water and atmosphere. For example, an example of coalbed methane development in Puchi anticline (Figure 3, Table 2).

In this area, the depressurization single-phase flow was completely discharged in the early stage, the gas, water and pulverized coal three-phase flow in the middle stage, the depressurization in the lower stage in the later stage, and the single-phase flow in the upper self-injection high-yield gas well, which basically maintained the status quo after 4 years. 477 vertical wells and 57 horizontal wells in this block have been mined for more than 4 years. At present, the vertical wells and horizontal wells with gas but no water production are 29%, 1 1% respectively, and those with water but no gas production are 12% and 19% respectively.

(2) Crossflow in the secondary accumulation of coalbed methane.

Cross-layer refers to the accumulation of desorbed gas to other horizons along faults, cracks or channels formed in the later stage during the exploitation of coalbed methane or when the upper part of goaf collapses. There are five main situations: (1) the original fault was closed in the early stage and opened after the pressure dropped to the critical point; (2) Horizontal wells penetrate roof and floor and faults; (3) The top and bottom plates are broken; (4) Cracks caused by mining stress release make desorbed gas penetrate the roof and floor and enter sandstone and limestone to form free gas; (5) After coal seam mining, the stress of roof caving is released, and a crack zone appears at the bottom.

Typical example analysis:

(1) The release of mining stress in Fuxin mining area leads to the formation of secondary reservoirs.

Mining and goaf: 7 wells have been drilled in Fuxin. After the goaf collapses, the daily gas production of a single well in the sandstone fracture zone at the top of the coal seam is1.5000 m3 ~ 21.5000 m3, and the CH4 content is more than 50%. After 1 year production, the cumulative gas production of a single well reaches 2.6 million m3. Yangquan's annual gas production is 765.438+06 billion m3, of which 90% is extracted from adjacent layers. 70% of Tiefa coalbed methane is produced in the mining area (Figure 4).

Fig. 3 Characteristic map of coalbed methane development in Puchi anticline

Table 2 Development of development wells in Puchi anticline

Note: The numerator in the column of daily gas production and daily water production is the output four years ago, and the denominator is the current output.

Fig. 4 schematic diagram of coalbed methane mining in mine and goaf

(2) Fracture channeling in vertical wells

The fracturing of well Punan 3 ~ 8 shows an ultra-low fracturing pressure of 9.6MPa, which is lower than that of adjacent wells by more than 10 MPa. At first, the daily water production was 62 m3, but now it is 54.8m3 four years later, and the cumulative gas production is only 38,000m3.

(3) Horizontal well channeling

FZP03~ 1 Well coal seam footage is 4084m, and drilling speed is 8 1%. The main branch and the branch have encountered four faults, which are obviously drilled into the lower water layer, and the development effect is poor (Figure 5): the maximum intermittent daily gas production 1366m3, the cumulative gas production is 290000m3, the cumulative water production is 43000m3, and the current daily gas production is 39000m3. The structural high point of the raw water layer is occupied by desorption gas. However, well FZP03-3, which is 75m shallower than this well, has a daily gas production of 3783m3 and a daily water production of 5m3.

In the exploration and development of coalbed methane, we should form a primary development well pattern to find the adsorbed gas in the coal seam and a secondary development well pattern to find the adsorbed gas in production. Due to the pressure drop in the mining process, hydrocarbons change from adsorbed state to free state to redistribute gas and water, break the original equilibrium state, and solve the exploration and development idea of gas channeling or channeling to form free gas reservoirs for secondary accumulation.

1.2 favorable coal-forming environment and high-yield enrichment cycle of coalbed methane

In oil and gas exploration, sedimentary facies were used to analyze the changing characteristics of sand bodies. Through a large number of coal seam clay mineral analysis, plant identification, logging characteristics, especially the whole coal seam coring observation, coal quality and gas-bearing analysis, it is considered that the influence of sedimentary environment on the generation, storage, preservation and permeability of coalbed methane is realized by controlling the composition of reservoir materials, and the sedimentary environment controls the heterogeneity in the layer and the micro-cycle of coal quality, and the heterogeneity of gas content and permeability in the layer.

Plane: Hejian Bay facies has thick coal seam, good coal quality, high gas content and high single well output, and the riverside highland is opposite to the lakeside depression (Table 3).

Fig. 5 schematic diagram of horizontal wells fzp03-1and FZP03-3.

Table 3 Data Sheet of Coal Quality and Output of C-P Different Coal Facies in Edong Gas Field

Vertically, due to the influence of sedimentary environment, thick coal seams often form multiple sedimentary cycles, including gangue, dark coal and bright coal, which has high vitrinite content, high permeability and high gas content. Different coal and rock components are controlled by coal-forming parent material types, and higher plants are abundant. The bright coal formed by gelation has low ash content, high vitrinite, developed cleavage and high gas content. Debris, water-soluble ions or dark coal in herbaceous coal-forming environment are the opposite.

Wushi 1 Well 9# coal can be divided into four intrastratal micro-cycles (Figure 6). Ash content: dark coal 14%~ 15%, bright coal 3.7% ~ 5.1%; Vitrinite content: dark coal 23%~49%, bright coal 66%~79%.

1.3 control of tectonic stress field on coalbed methane accumulation

In the high-value area of paleostress field, faults are developed, hydrodynamic force is active, coal seam mineralization is serious and gas content is low; The low-value area is characterized by well-developed coal seam fractures, confined water environment, good preservation conditions and high gas content. Local structural high points are often relatively low stress field areas, with high coal seam permeability, high single well production, good coalbed methane preservation conditions and high gas content without washing.

1.4 control of thermal evolution on pore structure of coalbed methane

The high rank coal is mainly composed of micropores less than 0.0 1μm and mesopores 0.0 1~ 1μm, generally more than 80%. Mesopores and micropores are the main adsorption spaces of coalbed methane, which are dredged by secondary cleavage and fractures.

Fig. 6 Sedimentary Cycle Diagram of Wushi 1 Well 9# Coal

Fig. 7 pore structure characteristics of high and low coal rank

Low coal rank >: 1μm is dominated by macropores and mesopores, with low evolution degree and undeveloped fractures. Macropore is the main storage space and diffusion, seepage and production channel of adsorbed gas and free gas.

The middle coal rank is dominated by medium and large pores, which is the diffusion and seepage channel of coalbed methane.

NMR: T2 relaxation time spectrum of coalbed methane reservoir has double peaks. Compared with the T2 relaxation time spectrum of conventional low permeability reservoirs, there is an obvious interval between the two peaks of coalbed methane reservoirs, which indicates that bound water and movable fluid cannot communicate effectively with coalbed methane reservoirs. However, the T2 spectrum structure of different coal rank reservoirs is different, which is due to the different pore structure (Figures 7 and 8). The low coal rank is dominated by macropores, while the high coal rank is dominated by micropores. The left peak of high coal rank curve peak coal seam is high and the right peak is low, the middle of the peak is zero, and the low coal rank is the opposite. The left peak is an immobile pore, and the right peak is a flowable secondary cleavage fractured reservoir. The higher the right peak value of high coal rank (cleavage development), the higher the gas well production (Figure 9).

1.5 control of hydrodynamic field on coalbed methane reservoir

Low water and high gas are produced in the stagnant area of local structural high points, and high water is produced in the pressure-bearing area of syncline. Groundwater is generally active in slopes and valleys, which conforms to the mechanism that water flows downwards and gas moves upwards. Most stagnant-weak flow areas in Fanzhuang block are >: 2500m3/d high-yield wells; The gas content in the eastern groundwater recharge area is 3/t, the gas saturation is 55%, the gas channeling is slow, and the single well output is 200~500m3/d (Figure 10).

2 characteristics of coalbed methane mining

For the medium and low permeability coal seams in China, the spacing between coalbed methane wells is generally 300m×300m, the stable production period of single well is 4~6 years, and the horizontal wells are shorter. Mining can be divided into three stages: rising period, stable period and declining period, and the declining period can be divided into several stages of gradual decline.

2. 1 The three types of mining characteristics are formed by the differences of heterogeneity in structural position and horizon.

Self-sufficiency: it is often located in areas with gentle structure and strong homogeneity. Gas production is the gas desorbed within the depressurization radius of the well. Drainage wells and production wells are generally located in the gentle part of the structure, with strong homogeneity in the layer. There are three stages of daily gas production increase-stable production-decline, and most of these wells are low-yield wells (Figure 1 1).

Fig. 8 pore distribution characteristics of different coal ranks

Fig. 9 T2 relaxation time spectrum of coal reservoirs with different rank.

Figure 10 Relationship between Groundwater, High Gas Content and CBM Production Area in Fanzhuang Block

Figure 1 1 single well exploitation characteristic map of coalbed methane

Outlet type: located in the wing of the structure, with strong heterogeneity. Part of the gas production is produced from the well through the depressurization and desorption radius of the well, and most of it is produced through the hypertonic channel or other wells along the upward trend. Drainage wells are generally located in the wing of the structure, with strong heterogeneity. Low or no daily gas production-rise-slow decline. Most of these wells have low production and rapid production decline.

Puchi anticline P1-1,PN 1- 1, PN2-5, HP1-kloc-0/0, HP2-1.

Input type: mostly located at the high point of structure. In the early stage, the depressurized desorption gas of the well is produced from the well through the depressurized funnel, and in the later stage, the desorption gas of the downtilt part of the structure is transported to the well for production. Drainage wells are located at structural high points, and these wells generally have a long period of high and stable production. Daily gas production increases-stabilizes-increases-decreases.

Well PN 1-4, P 1-3, PN2-7 and P 1-5, which are located at the high point of Puchi anticline structure, have high gas production and low water production, which are related to the diffusion and input of natural gas in the lower part, and have typical input production characteristics.

2.2 Different depressurization rates form three mining effects.

2.2. 1 unblocked desorption

The pumping liquid level is controlled reasonably, the depressurization speed is close to the desorption speed, the negative effect caused by effective stress is less than the positive effect caused by matrix shrinkage, the permeability increases-stabilizes with the generation of bound water and gas, and bubbles bring out some bound water, so the output is ideal (Figure 12-I). Taking Gu X- 1 well as an example, the drainage and production system of this well is reasonable. After half a year's drainage and depressurization, the liquid level is basically stable, and the daily gas production is stable above 4320m3/d, and it still maintains stable and high yield at present.

Figure 12 Characteristic curve of gas production influence of coalbed methane wells with different measures

Supercritical desorption

The desorption rate is lower than the depressurization rate, and the depressurization liquid level drops too fast, which leads to stress closure caused by coal seam cracks and cleat, and the daily gas production increases sharply-decreases sharply, the permeability decreases-stabilizes, and the gas production effect is poor (Figure 12-II). Take Gu Y-2 well as an example. After more than 30 days of drainage and depressurization, the liquid level of the well dropped below the coal seam. Because of the high pumping speed, the gas production effect in the early stage is poor. After the second adjustment of fracturing drainage system in July, 20 10, the maximum daily gas production reached 4000 m3/d, and it remained above 1600 m3/d in the later period. During the peak period of gas production, the daily liquid level of well PzP03 decreased by 63~87m, resulting in the highest single-well production (654.38+0.05 million) in China at the initial stage, and the single-well production in this area is the lowest at present.

Hindered desorption

The liquid dropping speed is too slow, the desorption rate is greater than the depressurization rate, the negative effect caused by effective stress is greater than the positive effect of matrix shrinkage, the bubble deformation and desorption are difficult, the desorption in the early stage of depressurization is blocked by pulverized coal, the liquid surface resistance desorption is not smooth, the daily gas production is unstable, and the development effect is poor (Figure 12-III). Well FzP03-3 was shut in for more than 26 times in 770 days, and the development effect was very poor.

2.3 types of coal seam water and its mining characteristics

Coal seam water can be divided into intralayer water, interlayer water and exogenous water; High-yield gas areas are intra-layer and inter-layer water, and water areas with external sources are low-yield gas areas.

(1) Formation water: water in coal seam cleavage and cracks. The daily water production is small, the high part is almost not produced in the middle and late stage of mining, and the low part is decreasing. The water in the formation can be further divided into four categories: movable water (fissure), adsorbed water (coal particle surface), wet water (in a capillary tube of-5cm) and crystal water (calcium carbonate).

(2) Interlayer water: thin interlayer water seeps into the coal seam. The water production in mining is obviously reduced and can be controlled.

Continuous depressurization of gas wells with interlayer water can control water production and improve development effect. Qinshui Fan Zhuang fzp 1- 1 The total footage of coal seam is 47 10m. It was put into production in April 2009, with the highest daily water production 175m3. At present, the daily gas production is 2 1436m3, the daily water production is 20.7m3, the casing pressure is 0. 15MPa, the liquid level is 4m, the cumulative water production is 37000m3, and the cumulative gas production is 8 14m3. It can be seen that in the case of interlayer water entering coalbed methane wells, water displacement increases in the short term, and the daily gas production continues to rise in the later period, and the development effect is good.

(3) Exogenous water: faults or fractures are connected with high permeability Ordovician limestone water and other water layers. The water yield is large and difficult to control.

3 CBM exploration and development of applicable technology analysis

3. 1 seismic AVO technology to predict high-yield and enriched areas

There is a great difference in wave impedance between coal seam and surrounding rock, and the reflection of coal seam itself is strong. The difference between gas-bearing and water-bearing is prominent in some places: after high gas content, the amplitude decreases with the increase of offset, resulting in AVO anomaly (bright spot), which is different from the concept of bright spot in which the high impedance amplitude of conventional natural gas increases with the increase of offset, and has the following characteristics: AVO anomaly in high production well strength (high gas content and low water content), unusually large intercept and gradient of coal seam profile, that is, strong bright spot; Weak AVO anomalies (low gas content and high water cut) in low-production wells are characterized by low gas content, low saturation and low permeability.

High AVO anomaly area in coalbed methane production area 1 well 5# coal gas content 2 1m3/t, daily gas production 2847m3 (figure13); The gas content of 5# coal in Jishi 4 well with weak AVO anomaly in low production area is 12m3, with daily gas production of 64m3 and water production of 90m3. According to this theory, seismic AVO technology can be used to predict high yield and enrichment areas.

Figure 13 Cumulative Stone 1 AVO Characteristic Map of Well 5# Coal.

3.2 Geological conditions applicable to directional pinnate horizontal well drilling

China has drilled more than 60 directional pinnate horizontal wells 160, and the maximum daily gas production of a single well is 10.5 million m3. Directional pinnate horizontal well technology is suitable for exploiting coalbed methane in low permeability reservoirs, which integrates drilling, completion and stimulation measures, and can communicate the natural fracture system in coal seam to the greatest extent, so that the single well production in the same area can be increased by 5~ 10 times. The applicable geological conditions are as follows:

(1) The structure is stable, and there are no major faults: FzP03- 1 encounters four faults, with the maximum daily gas production 1366m3, currently 687m3, and the daily water production is 32-75m3. The daily water production of wells 04, 07 and 09 in Hancheng is 20-48m3, and the daily gas production is less than 60.

(2) The sealing condition far away from the water layer is good: in September, the thickness of mudstone in the triple roof was 365,438+46,000m3, and no gas was produced.

(3) Bituminous structural coal is not developed: the average daily gas production of Hancheng and Heshun 12 wells is 720m3.

(4) The buried depth of coal seam is less than 1000m: the buried depth of coal seam is 800- 1000m, and the gas production per well is 3/-1FZ15-/kloc-0.

(5) coal seam thickness >; 5m: The coal seam of well CL-3 in Liulin is 4m thick, with a maximum daily gas production of 950,000m3, a steady production 1.60 days decreasing, a daily gas production of 2807m3, and a cumulative gas production 1.2 1.000 m3.

(6) gas content >; East of panzhuang 15m3/t: 8m3/t (cover thickness is 2~5m), and north 15~22m3/t (cover thickness >: 100 m), although the east is shallower than the north 100~200m.

(7) Main branch parallel coal seam or upward dip: average daily gas production of a single well, formation decline 1MPa stage accumulation and gas production effect analysis, horizontal well trajectory: parallel coal seam has the best occurrence, followed by upward dip and poor downward dip; "Convex" and "concave" types are the worst.

(8) Effective footage of coal seam > 3000m: footage of horizontal coal seam is 3, and cumulative gas production by stages is 3.

(9) The branch distribution is reasonable: the main branch length is about 1000m, the branch spacing is 200-300 m, and the included angle is10-20.

(10) Effective penetration rate of coal seam >: 85%: 10 wells, with 3 coal seam penetration rates, with a maximum of 3, and the average cumulative gas production at each stage is 270,000 m3.

3.3 Applicable conditions of ultra-short radius hydraulic jet drilling

This technology has drilled more than 23 coalbed methane wells in China, and the effect is not ideal. The main reasons are low permeability, small nozzle diameter, large bending and blockage after spraying; The diameter of hydraulic jet window is 28mm, and the aperture is small, so it is easy to be blocked by pulverized coal and water during drainage and mining. It can be used for rotary large-caliber nozzle and naked-eye injection test.

3.4 Applicable conditions for drilling "Shan", "U" and "V" wells

Because of the low permeability of coalbed methane reservoirs in China, and most of them belong to fault-block gas reservoirs, the area of coal seam connected by U-shaped horizontal wells is small, and the application effect is poor. Many U-shaped horizontal wells have been drilled 16 in China, and the stimulation effect is not obvious.

SJ 12- 1 stable daily gas production 1750m3, cumulative gas production 19 10000 m3, which has been decreasing for three and a half months. Running tubing and glass steel pipe in horizontal section is successful, but the effect of low permeability gas reservoir is poor. The high permeability area [(1.0 ~ 3.6 )×10-3μ m2] has a good effect: the daily gas production of single wells in Chang Bin and Sihe is 5600 ~ 1400 m3.

In the future, it is possible to test 1 horizontal wells in "Shan" well group to cross multiple vertical wells. At present, foreign countries have successfully developed salt rocks by using this technology.

4 conclusion

(1) According to the exploration and development practice of coalbed methane in China, the reservoir-forming modes of coalbed methane can be divided into three types: autogenous self-storage adsorption type, autogenous self-storage free type and endogenous external storage type; At the same time, it is considered that the accumulation period of coalbed methane can be divided into three types: early accumulation, late structural transformation and secondary accumulation in mining, and the secondary accumulation in mining will be the main production replacement field of secondary well pattern in coalbed methane development.

(2) Using sedimentary facies to analyze thick coal seams, high-quality coal seams and high-yield and enriched areas; By analyzing the microcirculation in thick coal seam, it is found that the coal-forming parent material controls the composition of coal and rock and the output of single well, and the bright coal formed by gelation has low ash, high vitrinite, developed cleat and high gas content, which is a high-yield enrichment section. Debris, water-soluble ions or dark coal in herbaceous coal-forming environment are the opposite.

(3) In the low-value area of paleostress field, coal seam cleavage is developed, and it is in confined water environment, with good preservation conditions and high gas content; The stagnant area produces low water and high gas, and the syncline pressure-bearing area produces high water.

(4) Heterogeneity differences between structural parts and strata form three mining characteristics: self-sufficiency, output and input, and different depressurization rates form three mining effects: stable, blocked and supercritical.

(5) AVO anomaly of high production well strength, that is, the strong point in the bright spot; AVO weak anomaly in low-production wells has the characteristics of low gas content, low saturation and low permeability. Directional pinnate horizontal wells can only achieve good development results under suitable geological conditions and drilling methods; Ultra-short radius hydraulic jet should be suitable for coal seams with high permeability, relatively stable coal seam structure and high gas content and saturation. U-type and V-type horizontal well drilling technology has poor effect in low permeability gas reservoirs and good effect in high permeability areas.

refer to

Chen Gang, Zhao Qingbo, Li Wuzhong, et al. 2009. Controlling effect of geostress field on high permeability area in Daning-Jixian area [J]. Geological Science, 2002. China Coalbed Methane, 6(3): 15~20.

Chen, Jia Chengzao, et al. 2007. Influence of tectonic uplift on the physical properties of high and low rank coalbed methane reservoirs [J]. Petroleum Exploration and Development, 34(4):46 1~464.

Chen, Yang Jiaosheng, et al. 2009. Analysis of key factors affecting the production of coalbed methane wells —— Taking Fanzhuang block in the south of Qinshui Basin as an example [J]. acta petrolei sinica, 30(3):409~4 12.

Deng Ze, Kang, et al. 2009. Dynamic change characteristics of coal reservoir permeability during development [J]. Journal of Coal Science, Vol.34, No.7: 947~95 1.

Kang, Deng Ze,. 2008. Discussion on drainage and production system of coalbed methane wells in China [J]. Natural Gas Geology, 19(3):423~426.

Li Jinhai, Su Xianbo, Lin Xiaoying, et al. 2009. Relationship between production and productivity of coalbed methane wells [J]. Journal of Coal Science, 34 (3): 376~380 pages

, Shen, Huang Hongchun, etc. 2007. Study on drilling technology of multi-branch horizontal wells in coalbed methane [J]. acta petrolei sinica, 28 (3):112 ~115.

Xi 'an Baoan, Li, Li, et al. 2005. Mining mechanism and application analysis of directional pinnate horizontal wells for coalbed methane [J]. Natural gas industry, 25 (1):14 ~117.

Zhao Qingbo, Chen Gang, Li Guizhong. 2009. Enrichment and high yield of coalbed methane in China, mining characteristics and applicable technologies for exploration and development [J]. Natural gas industry, 29(9): 13~ 19.

Zhao Qingbo, Li Guizhong, Sun Fenjin, et al. 2009. Evaluation theory and exploration technology of coalbed methane geological selection [M]. Beijing: Petroleum Industry Press.

CIF Dissel 1992. Coal-bearing sedimentary system-coal facies and sedimentary environment. Springer Publishing House. 19~22