Study on the Key Control Factors of Reservoir Formation in Slope Area and Its Guiding Practice for Well Placement

A35 block is located in the slope area of S1 nose-like structure, and the main target layer for development is the P formation in the Member 1 of Yaojia Formation of the Lower Cretaceous. 44.36 km2 of oil-bearing area is exploited in A35 block, with a geological reserve of 1025.0 × 104t. The geological structure is complex: the difference in elevation between the top surface of the east and west oil formation reaches 162.4 m, and the oil-water relationship is also complex: different parts of the same structure contain oil with large differences, and there is no uniform oil-water interface in the whole area. The block has a large proportion of drilling that encounters with the water-oil layers, which results in high water cut in the early production period and a large proportion of inefficient wells. What was worse, the original well network has a low control degree of water-flooding, due to the narrow sand body and the development of faults. In order to improve the effect of the overall development of the slope area, the study of multidisciplinary fine reservoir description needed to be deepened. At the same tine, the the analysis of the matching relationship between faults and sand bodies was innovatively used to evaluate the capacity of oil controlling of different traps and SGR algorithm was innovatively applied to quantitatively evaluate the lateral sealing ability of faults. Therefore, we can clarify the matching relationships between the faults and sand bodies which control the oil and gas accumulation in the slope area. Thus a total of 42 wells were able to be deployed for infilling and external expansion, further optimizing the well pattern and improving the relationship between injection and production. The degree of water drive control increased by 3.3% and the recovery rate increased by 2.3%, forming the first precedent of well pattern adjustment in the zone where water-oil layers are common.