With the deepening of oilfield development and the continuous improvement of reservoir description level, the understanding of oilfield geology is becoming more and more clear. In order to do a good job in the study of remaining oil distribution and improve oil recovery, it is necessary to divide the reservoir types carefully. The concept of fine reservoir type plays an important role in comprehensive geological research, fine reservoir description and remaining oil distribution in the later stage of oilfield development.

Reservoir description; Reservoir space; Closed unit; Reservoir type; Fine reservoir type

I. Introduction

With the subdivision of stratigraphic units by fine reservoir description, the method of determining reservoir types according to the trap genesis of a set of oil-bearing strata series can no longer reflect the reservoir characteristics of stratigraphic units well. In order to fully reflect the geological characteristics of each oil-bearing unit in an oil-bearing strata series, it is necessary to subdivide the reservoir types according to the accuracy of the described stratigraphic units in the process of fine reservoir description.

Second, the concept of fine reservoir types

Fine reservoir type [1] is put forward according to the different reservoir characteristics of different reservoir space closed units [2] in a set of oil-bearing strata, and it is a comprehensive synthesis of reservoir control factors on the basis of fine reservoir description. Its purpose is to distinguish different reservoir types more deeply and accurately and reflect their different characteristics. It requires that all geological control factors of oil-bearing units be integrated on the basis of closed units in reservoir space. The classification of general reservoir types emphasizes the main factors controlling reservoir formation and summarizes the overall characteristics of a set of oil-bearing strata. Simply put, fine reservoir type is a subdivision of a set of oil-bearing reservoir types.

Fine reservoir types can be widely used in the early stage of development plan formulation, comprehensive geological research in the late stage of development, fine reservoir description and other stages.

Three. Fine reservoir type classification

1. division

Fine reservoir classification [3] is an organic combination of trap genesis method and geometric shape method.

2. The principle of division

According to the principle that the main control factors, secondary control factors and geometric shapes are given priority step by step [4]. For the oil and gas reservoir formed by a closed reservoir space unit, if the main controlling factor is fault, it is named fault oil and gas reservoir first; If the controlling factor is the inversion trap formed by strata and faults, it is named inversion fault reservoir; If the reservoir is banded on the plane, it is named banded overthrust fault reservoir, such as the fine reservoir type of 92 small layer in the second member of Shahejie Formation in Xin 1 and 23 fault blocks.

3. Classification of reservoir types

The 6 ~ 9 sand groups of the second member of Shahejie Formation in 23 fault blocks in Xin 1 Hexin Oilfield are divided into three types of fine reservoirs (attached figure 1): banded inverted fault reservoirs; Lenticular overthrust fault reservoir; Updip pinchout lithologic reservoir. On this basis, reservoir evaluation is carried out according to fine reservoir type classification.

Figure 1 Fine Reservoir Type Classification Diagram

The upper Es4 reservoir in the east of Chunhua Oilfield is mainly controlled by structure, fault and lithology, and the fine reservoir types of each sublayer are obviously different, and the main oil-bearing sublayer is layered structure reservoir. The second major oil-bearing sublayer is a layered lithologic structural reservoir; The non-main oil-bearing sublayer is a layered lithologic reservoir or a layered structural reservoir.

4. Classification of reserves

According to the classification of fine reservoir types, the reserves of Xin 1 6 ~ 9 sand formations in the second member of Shahejie Formation 157 oil-bearing units and 23 fault blocks in Dongxin Oilfield are divided (table 1).

The lens overthrust fault reservoir has the largest petroleum geological reserves, which is 6 10.4× 104t, but there are too many oil-bearing sand bodies, and the geological reserves are not very concentrated, with an average of only 5.5×104t. For each oil-bearing unit. However, the oil geological reserve of banded overthrust fault reservoir is 456.9× 104t, but there are 19 oil-bearing units, and the average oil geological reserve of each oil-bearing unit is 24× 104t, which is relatively concentrated. The petroleum geological reserves of the updip pinchout lithologic reservoir are too small, and the average geological reserves of each oil-bearing unit are also very small, only 0.9× 104t. In this way, when making development well pattern or adjusting layer series, the banded top-down fault reservoir should be given priority, followed by lenticular top-down fault reservoir, and finally the updip pinch-out lithologic reservoir.

Table 1 Table of Fine Reservoir Types and Reserves of Sand Groups 6 ~ 9 and Fault Block 23 in the Second Member of Shahejie Formation in Dongxin Oilfield

5. Favorable block prediction

Fine reservoir types can guide the study of oil and gas accumulation law, which is of great significance to the prediction of favorable reservoir areas. According to the fine reservoir description, there are 20 1 and 157 oil-bearing units in the 6 ~ 9 sand formation of the second member of Shahejie Formation in Xin1area and 23 fault blocks in Dongxin Oilfield, respectively. According to the distribution and formation law of fine reservoir types, 44 oil-bearing units are predicted, and the predicted petroleum geological reserves are 68.5× 104t. The Xin 70-4 well area is predicted to be a lenticular overthrust fault reservoir, while the 92 sub-layer of the second member of Shahejie Formation in Xin 70-4 well is an oil-bearing water layer. A new well, Xin 70-X2 1, is deployed at the high position, with the estimated completion of drilling 10m and the actual drilling11m.. Initially put into production, with a daily output of 34.5t, the oil-bearing area is increased by 0. 1km2, and the petroleum geological reserve is increased by 13.3x 104t.

Four. conclusion

Fine reservoir types can be re-recognized from the perspectives of small layer, oil-bearing sand body, stratigraphic time unit and closed unit of reservoir space.

Fine reservoir types expand the application range of reservoir space closed units. The closed unit of reservoir space is the smallest concept of oil and gas trap. Its corresponding reservoir type is fine reservoir type.

Fine reservoir types provide a theoretical basis for fine calculation of reserves and help to solve the contradiction between injection and production in production; Guide the prediction of favorable oil-bearing areas of reservoirs.

The introduction of fine reservoir types makes clear the reservoir geological characteristics of oil-bearing calculation unit.

The concept of fine reservoir types enriches the content of reservoir types, which is of great significance to the comprehensive study of oilfield geology, the description of fine reservoirs and the study of remaining oil distribution in the later stage of development. Fine reservoir types based on closed units of reservoir space can understand the law of oil and gas accumulation from one side, study the law of reservoir formation in composite oil and gas areas, and guide the adjustment of tapping potential in old areas.

The application of fine reservoir types is still in the exploration stage, which needs to be continuously improved and developed in scientific research and production practice.

Main references

[1] Wang Duanping, Liu Qiang. Fine reservoir description in complex fault block oilfield. Acta petrolei sinica, 2000.

Sun Longde, Sun Chunlian. Geological transformation and design of high-yield and high-efficiency wells in complex fault-block oilfield. Proceedings of the international symposium on exploration technology of complex oil and gas reservoirs. Dongying: Petroleum University Press, 1998.

Zhang Houfu, Zhang Wanxuan. Petroleum geology. Beijing: Petroleum Industry Press, 1989.

Qiu Yinan is from Chen Ziqi. China reservoir management technical manual: reservoir description. Beijing: Petroleum Industry Press, 1996.