Study On Logging Evaluation Method For Validity Of Dabei High - Steep Structure Reservoir

In Dabei gas field, both high-steep structures and large formation-dip strata can be easily found. The lithology is complex, and natural fractures are developed. The strong stress which was caused by strong level of compression, gravity compaction and abnormal high pressure. The cretaceous glutenite reservoir is dense, with low porosity and permeability. So, the effectiveness of the reservoirs is poor. The existing conventional logging methods and techniques can not accurately calculate the situ stress of high-steep structures, and evaluate the effectiveness of reservoir fully and effectively. Result of well logging interpretation and evaluation often conflict with the actual test results.Put the relations of situ stress and reservoir validity as the main line, and carried out five aspects research work in view of Klbs stratum:(1)Core stress experiment, nuclear magnetic resonance (NMR) and litho-electric experiment;(2)Eextracted of p and s wave, and construct the s moveout for which well has no DSI date. Research on the calculation method of rock mechanics parameters;(3)Analyzed logging response characteristics of situ stress of high-steep structure; Considered the influence of stratum dip and fracture on the situ stress; Established the quantitative calculation model about situ stress of high-steep structure, and calculated the level stress accurately;(4)Researched the relationship between situ stress and reservoir validity with linking reservoir geological characteristics and logging reservoir evaluation results. In order to clear reservoir validity’s control factors of low density fractured sandstone reservoir;(5) Extracted the discriminant index, and to establish the validity of reservoir discriminant chart. By dealing with well data effectively and visually determine the effectiveness of the work area reservoirs. Through the study of key problem deeply, achieved the following results and understanding:1. By analyzed the three experimental results, the following contents were been found. The difference of level stress is large, and natural fractures are developed at Klbs in dabei302well. The porosity and permeability are very low, rock electrical parameters m and n have great hanges. Magnetic saturation is high. Because the majority of small diameter pores, pore throat connectivity and permeability are poor. The reservoir validity is not good enough.2. Stratum dip makes the situ stress get large, and the effect of fracture dip is opposite. The stratum dip angle increases the overburden pressure and the anisotropy of rock. The effect on situ stress is large while it is big, and vice versa. Fracture dip also have great influence to the calculation of situ stress when it becomes larger.3. The matrix porosity and matrix permeability of rock becomes down, when the effective stress and difference of flat stress are rising. The porosity and the width of fracture are decreasing with the effective stress increase. The open degree of fracture would get better when the angle β is less than45, which is angle between the fracture trend and the direction of the modern maximum stress. It contributes to stratum of reservoir space, and reservoir validity comes better.4. Good reservoir appear in well interval which has low effective stress and effective stress ratio and horizontal stress difference. When the angle β between the fracture trend and the direction of the modern maximum stress is smaller, fracture is more development. Difference of trend stress (SH12*COSB) which is the product of flat stress and cosine of B is larger, fracture is more development. The porosity and the width of fracture become big, and reservoir validity will get better.Based on foregoing research, a suit of logging evaluation methods and techniques has been formed which about the relationship between stress and the reservoir effectiveness. The evaluation results of reservoir effectiveness were good, judging from processing results of the wells logging data. And it provided a reliable geological basis for oil test, acidification and fracturing, etc.