(1. China Youshi University (East China), Qingdao, Shandong 266555; 2. School of Resources, China Geo University (Wuhan), Wuhan, Hubei 430074; 3. Exploration and Development Research Institute of TUHA Oilfield Company, Hami, Xinjiang 839009)
Abstract: The natural gas of Shuixigou Formation in Kekeya area at the northern foot of Turpan-Hami Basin is produced in tight sandstone reservoirs, with an average porosity of 4.8% and an average permeability of 0.07× 10-3μm2 (the permeability of overlying strata is less than 0.02× 10-3μm2). The exploration and development of Kekeya gas reservoir shows that under similar wellbore technical conditions, the single well production of exploration wells and development wells with different sand body genetic types and structural parts is quite different. By studying the characteristics of sedimentary facies belt, genetic types of sand bodies with different genetic factors, rock composition, diagenetic evolution, plastic cuttings and argillaceous content of tight sandstone, it is considered that the comprehensive influence of various factors is reflected in the grain size of sandstone, the distribution of high-yield belt is controlled by the coarse facies belt of reservoir (near the mainstream line), and the development of structural highs and fractures on the plane is also an important factor to determine oil and gas enrichment and natural gas productivity. Through the analysis of productivity control factors, the distribution of favorable reservoir facies zones and high-yield enrichment zones is predicted, and the control factors of natural gas reservoirs are clarified, which has a good guiding significance for the exploration and development of tight sandstone gas in Kekeya area.
Key words: tight sandstone gas; Sedimentary reservoir; Reservoir controlling factors
Sedimentary reservoir characteristics and reservoir control factors of tight sandstone gas reservoir in Shuixigou Formation in Kekeya area
Song Yukai 13, Wang Jinsong 2, 3, Pan Hongfang 3, Liu Huchuang 3, Hu Jun 3.
(1, China Shiyou University, Qingdao, Shandong 266555; 2. School of Resources, China Geo University, Wuhan, Hubei 430074; 3. Exploration and Development Research Institute of TUHA Oilfield Company, Hami, Xinjiang 839009)
Abstract: The natural gas of Shuixigou Formation in Kekeya area in the northern piedmont of Turpan-Hami Basin is mainly concentrated in tight sandstone reservoirs. Its average porosity and permeability are 4.8% and 0.07× 10-3μm2 respectively (the permeability of overburden is less than 0.02× 10-3μm2). The gas reservoir exploration in this area shows that under similar borehole technical conditions, the single well production is very different between exploration wells and development wells due to different sand body genetic types and different structural levels. The sedimentary facies characteristics, genetic types, rock composition, diagenetic evolution, plastic cuttings and argillaceous content of tight sandstone are studied. It is considered that the grain size of sandstone is the key factor, the coarse facies zone (close to the main stream line) controls the distribution of productive zones, and the high structure and fracture development in the plane are the important factors to determine oil and gas accumulation and natural gas production. On the basis of analyzing the factors affecting production control, the favorable reservoir facies zones and high enrichment zones are predicted, and the reservoir control factors of natural gas are recognized. It has guiding significance for the exploration and development of tight sandstone gas in Kekeya area.
Key words: tight sandstone gas; Sedimentary reservoir; Reservoir controlling factors
Kekeya area is located in the middle of Beishan foreland belt in Taibei sag of Turpan-Hami basin, which is a foreland thrust fold belt in Turpan-Hami basin. After oil and gas exploration in recent years, many gas-bearing structures such as K 19, K2 1, K24, K28, J2x, J 1s, J 1b655 have been discovered in Kekeya area. Among them, J 1b 1 and J 1b2 are the most important gas-bearing series, and the Kekeya area has already had the initial production capacity in the development of the past two years. Judging from the drilling results of exploration wells and development wells at present, there are great differences in natural gas enrichment degree and single well production in different regions, different horizons, different geological conditions and different gas reservoirs. This paper mainly analyzes the controlling factors of enrichment and high production of tight sandstone gas reservoirs from the aspects of sedimentary facies belt, structural background, maturity of rock composition, fracture development degree and its configuration relationship. Through the description of the plane distribution of main geological conditions, the Kekeya gas reservoir is deeply studied, and the favorable natural gas high-yield enrichment zone is predicted, which provides a basis for expanding the exploration area in the next step.
Basic characteristics of gas reservoirs in 1 Kekeya area
Under the long-term paleosedimentary landform of slow south and steep north, Taibei sag has formed a stratigraphic distribution pattern of thick north and thin south. During the sedimentary period of Shuixigou Group, a set of large coal measures strata was formed in Kekeya area in the northern piedmont zone, with a thickness of 500 ~ 1100 m. Under the long-term burial state of foreland depression, the evolution maturity of source rocks is the highest, and the highest Ro can reach1. The Lower Jurassic in Kekeya is mainly composed of braided river delta sedimentary sand bodies with northern provenance, and the main gas reservoir sand bodies are medium sandstone and coarse sandstone of underwater distributary channel at the front of braided river delta, with large thickness and stable lateral distribution. The peak value of reservoir porosity is 4% ~ 6%, the peak value of permeability is (0. 1 ~ 0.5) × 10-3 μ m2, and the permeability of overburden is less than. The source rocks of Shuixigou Group in this area are in close contact with the reservoir in a large area, and the source reservoir is in a "thousand-layer cake" structure. The analysis shows that Kekeya gas reservoir has typical characteristics of post-formed tight sandstone gas reservoir.
There are three sets of gas reservoirs in Shuixigou Formation in Kekeya area, with the buried depth of 2800 ~ 4300m .. J 1s gas reservoir: the average thickness of single layer is18.4m; ; J 1b gas reservoir: the average thickness of single layer is 55.2m, and the daily gas production of single well is (1.9 ~ 7.6) ×104m3; J 1b gas reservoir: the average thickness of single layer is 49.6m, and the daily gas production of single well is (2.9 ~ 5.9) ×104m3; Cumulative thickness105 ~ 280m. The statistical analysis of single well production and gas-bearing property shows that the enrichment and high yield of gas reservoirs in Kekeya area have the following laws:
(1) For the reservoir located under the main source rock coal seam, the closer the sedimentary facies belt is to the river, the coarser the sandstone grain size, the higher the gas production and the richer the natural gas, such as J 1b 1 gas reservoir 3393.8 ~ 34 10m interval of well K 19. After acidification, a high-yield oil gas flow with a daily output of 3,060 appears, while a low-yield natural gas gas flow of 3,600 m3/d is obtained after acidification in the J 1b 1 gas-poor layer 3991~ 3,999 m interval of Well K23. The core particle size statistics show that its coarse and medium particle fractions occupy the main peak. After oil testing, only a small amount of water was found in J 1b 1 and J1B Ⅲ oil and gas display sections of Well K22, and the oil testing result was dry layer with medium-fine to fine-grained rocks. According to the analysis, the reservoir of this well is mainly deposited in estuary dam and distributary bay. On the other hand, the gas layer in J 1b interval 313 ~ 3177m of well K24 is close to the coal seam. Microscopic observation shows that there are a large number of intergranular pores and intragranular dissolved pores in rocks, and the phenomenon of increasing intragranular dissolved pores is also very common, but it is far from 3 16 1 ~ 366 coal seam section.
(2) High-yield gas reservoirs are closely related to structural positions and fracture development. Comparing the gas reservoirs of Badaowan, the main natural gas exploration well in K 19 block, it can be seen that the gas test production of K19/and K 19-6 in the high part of the structure is the highest, and the gas production of K 19-6 well is close to 8×1. The reason for the high yield in the high part of the structure is that cracks and micro-cracks occur in the strata in the high part of the structure, which improves the connectivity of pores in the rock, which is also confirmed by core observation. In wells located in the high part of the structure, fractures usually develop in reservoir rocks. There are 78 core fractures in K 1 well 65438+ 14.99m, with an average fracture density of 5.2 fractures/m. After fracturing, the daily gas production is 9.79× 104m3 and the oil production is 7. 15t. Microscopic observation of these wells also shows that, however, in the lower part of the structure,
Distribution characteristics of sedimentary system and reservoir sand body
The research results of sedimentary background show that during the Jurassic sedimentary period, the paleogeomorphic pattern of "one uplift and two depressions" formed in the northern piedmont zone controlled the direction of water flow and the distribution of sand bodies, and there was an underwater highland along the ws 1-A2 well, which divided Taibei sag into two parts, obviously controlling the distribution of sedimentary sand bodies and oil and gas accumulation in this area, and Kekeya area was located in the northwest wing of this underwater highland. The transition zone between highland and sag, therefore, this area has good conditions for the development of source rocks, sandstone reservoirs and facies belts. The northern provenance is the main provenance in this area, and the main target layers are the sedimentary system types of Badaowan Formation and Sangonghe Formation, including braided river delta, normal delta and lake sedimentary system. Sedimentary sand bodies are mainly underwater distributary channel, estuary bar sand bodies and a small amount of turbidite sand bodies, and thick sand bodies are mostly composed of sand bodies with different origins.
2. 1 reservoir sedimentary system
According to the analysis of sedimentary characteristics, the Shuixigou Group in Kekeya area has developed a thick floodplain and coal-bearing formations in the lake bay.
Sedimentary period of the second member of Badaowan Formation: the northern piedmont zone is gentle, and the sedimentary system is mainly rivers, deltas and shallow lakes. At the same time, swamps are widely distributed in floodplains, delta plains and coastal shallow lakes, and a set of coal-bearing clastic rocks are accumulated. Cocoa area is mainly composed of braided river delta front subfacies (figure 1). Based on the study of J 1b2 seismic facies of Badaowan Formation, the main sand body sedimentary types in Kekeya structural belt and its north are braided river delta front underwater distributary channel and estuary bar microfacies. The thickness of sand body increases from south to north, and the sand body in the north is highly enriched, and the sand body is distributed in a contiguous pattern. There are mainly four water systems in Kekeya structure and J 1b2 in the northern area, among which the water system in the northern part of Well K22 is large, the sand body is highly enriched and develops continuously, and the development scale of sand body in the southern part is weakened.
Figure 1 Sedimentary facies map of Beishan front zone in Taibei Depression J 1b2
The sedimentary period of the first member of Badaowan Formation: similar to the sedimentary characteristics of the second member, it is still a very shallow sedimentary environment. The northern piedmont sedimentary system is mainly braided river delta-shore shallow lake, and the distribution range of sand bodies is similar to that of the second member. In Kekeya area, two sets of water systems developed in the north extend to the south. Well K22 has a large water system in the north, high sand body enrichment and continuous development, while the sand body development scale in the south is weakened.
Sedimentary period of Sangonghe Formation: the lake basin is enlarged, and the lake basin is still a gentle shallow water sedimentary pattern. The steep slope in Kekeya area shows the sedimentary environment of shallow lake in front of braided river delta.
2.2 Plane distribution of sand bodies
According to the seven middle-cycle sand layers divided by the first and second members of Badaowan Formation in Kekeya area, the formula of natural gamma-particle size median relationship is adopted:
Proceedings of the International Conference on Unconventional Oil and Gas Exploration and Development (Qingdao)
Where: x is the median particle size; Y is the gamma logging value.
Using the grain size median-natural gamma relation table, the plan drawn by counting the proportion of coarse sandstone in each sand layer of each well in the plane can reflect the general position of the main channel of the river and the main enrichment area of delta sand bodies during the sedimentary period. Among them, the high-value areas of coarse sandstone content in the fourth sand group of the second member of Badaowan Formation are concentrated in H3, K22, K 19, K23 and other areas, indicating that four water systems developed from north to south in this period, and the distribution of coarse sandstone content showed a trend of increasing from the basin edge to the depression slope area and then decreasing to the center of the depression. The thickness distribution of sandstone in the second member and the third member of Badaowan Formation and the inherited development of the fourth sand group, K27, K28, K22, K 19 and K23 are inherited thick sandstone distribution areas; The high-value area of sandstone thickness in the second member of Badaowan Formation is mainly distributed in Well K22, Well K 19 and Well K23, and the accumulated thickness of sandstone is greater than that in Sand Groups 3 and 4. During the deposition period of Sand Group 2, the influence range of terrigenous clastic system in the north tends to expand and thicken southward, and the thickness of sandstone in Well K23 is relatively large, with the maximum reaching over 70m. The thickness distribution of sandstone in the second member of Badaowan Formation 1 sand formation is quite different from that in Ersha Formation. The high-value area of sandstone thickness is mainly distributed in well K27 and well K 19, and the accumulated thickness of sandstone is thinner than that of the second sand group. It can be seen that, during this period, the influence scope of the northern terrigenous clastic system tends to decrease northward, especially in well K22. The No.3 sand layer in the first member of Badaowan Formation is in the initial stage of rising after the base level drops, so the high-value areas of sandstone thickness are widely distributed, mainly in well areas K27, K20, K 19 and K23, and the thickness increases. The distribution of high-value area of sandstone thickness in the first member of Badaowan Formation is limited, only in K20 and K 19 well areas, and the influence range of terrigenous clastic system in the north is rapidly reduced to the north. In the first member of Badaowan Formation 1 sand formation, terrigenous detritus has the least influence on Kekeya, and the cumulative thickness of medium-fine and above sandstone is generally 10 ~30m, and the distribution of high-value areas is limited, only in well areas K20, K 19 and K23.
Analysis of reservoir performance and its main controlling factors
3. Physical characteristics of1j1b reservoir
J 1b is the only major reservoir for large-scale accumulation in Kekeya area. According to the statistical results of conventional physical property analysis data of 2 19 cores in this area, the porosity of Badaowan Formation is between 2.2% and 8.4%, with an average of 4.8%, and the porosity of most samples is between 3.0% and 7.0%. The permeability is (0.002 ~ 3.614 )×10-3 μ m2, with an average of 0.070× 10-3μm2. The permeability of most samples is less than 0.640× 10-3μm2 (Figure 2), while the permeability of covering layer is 0.
The effective porosity of the gas-bearing sand layer in the first member of Badaowan Formation ranges from 4.3% to 8.4%, with an average of 5.9%, and the permeability ranges from 0.077×10-3.6 μ m214×10-3 μ m2, with an average of 0.373×/kloc. The porosity of a few samples is 8.0% ~ 10.0%, the permeability is1.00×10-3 μ m2 ~/kloc-0 10.00×10-3 μ m2, and the permeability is greater than/kloc-0. Overall, this set of reservoirs has ultra-low porosity and ultra-low permeability. The porosity of the second member of Badaowan Formation ranges from 2.5% to 6.3%, with an average of 4.7%, and the permeability ranges from 0.002×10-3 μ m2-1.123×10-3 μ m2. The effective porosity of gas-bearing sand layer is between 4. 1%-6.3%, with an average of 5. 1%, and the permeability is 0.002×10-3 μ m2 ~1.123×/kloc-0.
Fig. 2 Histogram of reservoir physical properties of Badaowan Formation in Kekeya area
3.2 Analysis of reservoir dynamic main control factors
The experimental analysis data show that the sedimentary facies zone of the reservoir in Kekeya area determines the original reservoir performance of rocks, and the plastic cuttings and illite content of rocks are the most important factors affecting the reservoir performance, which are mainly reflected in the grain size of sandstone, and the grain size is the main parameter determining the reservoir performance, followed by the strength of diagenesis.
3.2. 1 control of sedimentary facies zone on reservoir properties
The lower Jurassic sedimentary system in Kekeya area belongs to a typical braided river delta sedimentary system. The genetic types of sand bodies are mainly underwater distributary channel, estuary bar sand body and a small amount of turbidite sand body, and sedimentation has obvious control effect on reservoir granularity. The middle and lower part of underwater distributary channel and the upper part of estuary dam are favorable reservoir facies zones with good physical properties, especially permeability. In the facies belt with coarse lithology, the hydrodynamic force is strong, the maturity of mineral components is high, the content of plastic cuttings is low, the content of illite is also low, and the content of matrix is even lower. For example, Well K 19 is located near the delta trunk line, with coarse lithology and obviously good physical properties (Figure 3). Well K20 is located at the side edge of the delta, and its physical properties are deviated, especially well K22, whose core is medium-fine sandstone, the relative content of illite is as high as 93%, and the permeability is mostly less than 0.05× 10-3μm2.
3.2.2 Petrological characteristics and reservoir performance of reservoirs
The reservoir of Shuixigou Formation in Kekeya area is characterized by low compositional maturity, high structural maturity, low interstitial content, developed dissolution and widespread illite in interstitial materials. The cuttings of Badaowan Group are mainly composed of pyroclastic rocks, magma and metamorphic rocks, accounting for 50% ~ 65% in general. Under the background of strong compaction diagenesis, plastic cuttings (phyllite, low metamorphic mudstone and slate) in cuttings are prone to compaction deformation, especially phyllite, which strongly destroys primary pores and causes a sharp decline in porosity and permeability. There is a good correlation between plastic cuttings content and porosity and permeability.
In addition, illite content is also closely related to reservoir performance. Generally speaking, the lower the illite content, the better the reservoir performance. The clay minerals in Badaowan Formation are mainly illite, with a relative content of 63% ~ 92%, followed by illite mixed layer, accounting for about 65,438+00%, and other clay minerals are relatively low. Illite often occupies the position of pores and throats, which has a great influence on physical properties.
3.2.3 Grain size is the main influencing factor of reservoir performance.
The relative content of plastic cuttings and illite is still determined by the grain size of sandstone minerals. The coarser the particle size, the lower the content of plastic cuttings and the better the reservoir performance. The lower the relative content of illite in sandstone clay minerals with the same particle size, the better the physical properties. Therefore, the grain size is the real control parameter that determines the reservoir performance. The coarser the grain size, the better the reservoir physical properties. Particle size has a good correlation with porosity, but it has a poor correlation with permeability, mainly because the pore types in this area are mainly dissolved pores, with few intergranular pores, most of which are filled with illite and micro-fractures.
In addition, the grain size of sandstone determines the pore structure. Coarse-grained sandstone has strong compressive capacity, low clay mineral content, more reserved pores and throats, and good matching relationship between pores and throats. The coarser the particle size, the larger the throat radius and the lower the displacement pressure. Pore structure determines the permeability of reservoir matrix, and the better the pore structure, the higher the reservoir permeability.
3.2.4 Influence factors of diagenesis on reservoir physical properties
Diagenetic compaction and pressure solution are the main reasons for the decline of reservoir performance of Badaowan Formation in this area. Due to the influence of organic acids in early rapid burial and diagenesis, the clastic particles of reservoir sandstone in Badaowan Formation were crushed and broken, which made the particles contact closely. In addition, there is pressure dissolution at the particle contact point, especially at the timely particle contact point. Due to the action of organic acids, pressure dissolution is promoted, and the point contact between particles gradually evolves into line contact and concave-convex contact; The cementation type evolved from pore type to pressure embedding type. Dissolved components and pressure-soluble components are mainly filled in granular dissolved pores and residual intergranular pores in the form of time-dependent secondary enlargement, microcrystalline time-dependent and flaky illite clay.
Whether the fluid flow in reservoir is smooth or not has obvious influence on diagenesis. Whether the fluid flows smoothly in sandstone affects the types of authigenic clay minerals. For the diagenetic evolution of reservoir sandstone with obvious acid formation water action (coal measures strata), compaction, pressure dissolution and dissolution of feldspar and other clastic particles are strong.
From the above analysis, it can be seen that the reservoir granularity is the real controlling factor that determines the reservoir performance, and the coarser the granularity, the better the reservoir physical properties. Sedimentary facies determines the grain size of sandstone, and coarse-grained glutenite is mostly located in the middle and lower part of underwater distributary channel and the upper part of braided river delta estuary dam.
Fig. 3k 19 1 Comprehensive histogram of sedimentary reservoir in coring section of well.
Analysis of reservoir control factors and prediction of favorable zones
4. The1structural belt contains gas as a whole, and the structural background (high part of the structure) controls the natural gas enrichment.
Since the formation of the Kekeya structural belt in Yanshan period, the oil generated by Jurassic in both depressions began to accumulate, and the natural gas generated by Jurassic in Himalayan period began to accumulate. The isomorphism of faults and sand bodies forms the transport system of oil and gas migration, and traps such as fault anticlines and fault blocks are good places for natural gas accumulation.
The natural gas enrichment and high production of coarse-grained sand bodies in Badaowan Formation in this area are basically controlled by traps such as fault anticlines and fault blocks, and the gas production of sand bodies in the trap range is generally high. However, the lateral shielding ability of the fault is relatively poor, oil and gas will not completely fill the trap range, and the lower part basically contains no gas. For example, the sealing degree of fault block in K 19 well area is 620m, but the height of gas column is only about 200m; The height of gas column in K23 block is 200m, and that in K24 block is 250m. In addition, the fault sealing is not enough to seal the gas reservoir with too high gas column height, and it is not easy to form a large-scale high-yield gas reservoir in the fault development area. Generally speaking, the structural background (high structural position) in this area controls the enrichment of natural gas.
The results of gas logging and gas testing in Kekeya area show that 27 exploration wells and development wells in this area generally contain gas, and the structure and sedimentary coarse facies zone have obvious control effect on production. High-yield wells are mainly located in the overlapping area of fracture development zone and coarse facies zone in the high part of the structure. According to the well 19 tested in this area, high-yield wells and industrial gas wells such as K24, K 19 and K19 are mainly located in the high part of the structural axis, and their fractures are also developed. On the contrary, Badaowan Formation of Well K 19-3, which has the same lithology and physical properties as Well K19, only produces 1008m3 of natural gas per day after fracturing. The well is located in the wing of the structure, with undeveloped fractures and poor fracturing effect.
4.2 The grain size of sandstone, the degree of fracture development and its configuration relationship determine the productivity.
From the gas test results and core observation, under basically the same structural conditions, the reservoir section of high-yield wells is not only coarse in lithology, good in physical properties, but also developed in fractures. The most typical example is that after acidizing in the 3113 ~ 3120m interval of well K24, the daily output of condensate oil is 7.46t, the natural gas is 208800m3, and the water is 5.44m3 The reservoir with coarse grain size and developed fractures is generally middle-grade. For example, after fracturing in section 3393.8 ~ 34 10m of well k 100, and acidizing in section 3460 ~ 3475m of well K2 1 00, the daily oil production is 5.04 tons, gas is 22026 cubic meters, and water is 7. 12 cubic meters. Reservoirs with fine grain size and undeveloped fractures are generally dry layers. Well K22 is 368 1 ~ 3688 m acidizing and fracturing without producing fluid. Therefore, the effective cooperation between sandstone coarse facies zone and fracture development zone is the key factor to obtain high productivity.
On the plane, the coarse facies zone (near the main stream line) controls the distribution of high-yield natural gas zones. The overlay of the distribution range of coarse sandstone and the oil test results in Kekeya area shows that most of the high-yield wells are distributed in the main river channel under basically the same structural background, and the grain size of sand body is relatively coarse, and the grain size of sandstone is the basis for determining productivity (Figure 4).
Figure 4j 1b 22 Isogram of Coarse Sandstone/Formation Thickness Ratio
4.3 Prediction of Favorable Zones in Kekeya Region
Through the analysis of the controlling factors affecting the reservoir and productivity of Kekeya gas reservoir, the controlling factors of high-yield layer are clarified, and the distribution of favorable reservoir facies zones and high-yield enrichment zones is effectively predicted. In the prediction and optimization of favorable facies belt, the basis of selection is: (1) sedimentary facies belt, preferably braided river delta front area; (2) The coarse-medium grain size area is selected for the grain size of reservoir minerals; (3) The most effective part is the selection of structural background in structural anticline, nose structure, slope area and fracture development area. The above three factors are superimposed on the plane to determine the favorable zones, and the distribution of the favorable zones of two main reservoirs J 1b 13 and J 1b2 1 in Kekeya area is predicted emphatically.
J 1b 13, main gas interval: the structural favorable areas mainly follow the lines K 19-K20 and K2 1-K24-H3, and two favorable areas can be selected in combination with the fracture development area and coal and rock distribution area over 20 ~ 30m;
Class I favorable area: located in the slope area of tectonic uplift, with developed fractures, thick coal and rock at the top of Badaowan Formation, and this area belongs to coarse sandstone distribution area. At present, K2 1 in this area has obtained industrial airflow in J 1b3 sand layer.
Class II favorable area: located in the tectonic uplift area with developed cracks. At present, K20 and K 19-6 obtain high-yield oil and gas flow at J 1b 13, which belongs to the area between the inner front and the outer front of braided river delta, and the thickness of sand body and top coal and rock changes greatly.
J 1b2 1 main gas interval: the structural favorable areas mainly follow the lines of K 19-K20 and K2 1-K24-H3, and two favorable areas can be selected in combination with the fracture development area and coal and rock distribution area over 20-30m;
Class I favorable area: located in the slope area of tectonic uplift, with developed fractures, thick coal and rock at the top of Badaowan Formation, and this area belongs to coarse sandstone distribution area. At present, there is no industrial airflow in J 1b2 1 sand layer in this area.
Class II favorable area: located in the tectonic uplift area with developed cracks. At present, K 19, K20 and K 19 -6 have obtained high-yield oil gas streams. Due to the invasion of lake water, the thickness of sand body and top coal rock in this area changes greatly, and K 19-3 and K 19-4 are both low-yield.
5 conclusion
Shuixigou Formation gas reservoir in Kekeya area (1) is a typical tight sandstone gas reservoir, and its abundance and single-well natural gas productivity are obviously different according to structural location, sedimentary facies zone and fracture development.
(2) The sedimentary facies belts of the main gas reservoirs in Kekeya, such as J 1b 1, J 1b2 and J 1s, are mainly braided river delta front-shallow lake, and the main reservoirs are braided river delta front underwater distributary channel, estuary bar sand body and a small amount of turbidite sand body.
(3) The sedimentary facies zone of the reservoir determines the primary reservoir performance of the rock, and the content of plastic cuttings and illite in the rock is the most important factor affecting the reservoir performance, which is mainly reflected in the grain size of sandstone, and the grain size is the main parameter determining the reservoir performance, followed by the strength of diagenesis.
(4) The enrichment and high production of oil and gas are controlled by sedimentary facies belt, structural high points, sand body granularity, fractures and other factors. The whole Kekeya structural belt contains gas, and the high part of the structure is the main rich area of natural gas. The coarse facies zone (near the main flow line) controls the distribution of high-yield zones, and the relationship with fracture development and morphology determines the natural gas productivity.
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