Drilling Geological Characteristics Of The Western Sichuan Region Logging Study

The technology about the logging identity the geologic character of drilling is an important content of synthesizing speedily and high quality drilling. The geologic character description about drilling includes lithology, rock mechanic parameter, drillability, abrasivity, crustal stress and three stratum pressure etc. There is gigantic thick land facies clastic rock layer about Jurassic system and Upper Triassic in the sunken of Chuan-xi. From above to below there are Peng Lai-zhen group, Sha Xi-miao group, Qian Fou-ya group and Xu Jia-he group four gas reservoir. Taking T₃X² as the main aim layer in Upper Triassic, the wells depth is 4600-5700m, which is the important exploitation aim using enlarging reserves at present.The engineering geology character is complex, which showing is that there are many producing layers and many series pressure system. When drilling to Peng Lai-zhen group, the high pressure gas layers are developing, the geologic structure is complex , the shallow stratum is discortant contact, the stratum is breaked , the argillutite hydrating is easy, the coal bed of deep Xu Jia-he stratum is instability which will collapse, and the fracture and rupture are developing which will cause the windows of drill fluid become narrow and the stability become poor, all that will cause "blowout,leak,block and collapse" etc drilling accident. When drilling to below Sha Xi-miao and Xu Jia-he stratum, the lithology is very compact and hardness, which cause the abrasivity become strong and the drillability become poor, all these cause the drilling speed is slow and the drilling period is long and bit selection is difficult.Since well logging data implies large geologic environment facts information, and has the merits of high definition, fine continuance, convenient and economic etc. So we need using log information lucubrate the drilling engineering geology feature of the drilled wells or the undrilled wells.This paper adopts MMMA analysis method calculating the volume content about the rock mineral and founding the lithology volume section in work area. Based on rock mechanics test demarcates the rock mechanics of logging calculating and founding the rock mechanics parameters section. All which will offer the lithology and rock mechanics parameters about bit selection,crustal stress and stratum pressure.Based on the test of drillability and the rock drillability drawing from logging, the stratum drillability section will established. Combining the drilling practice and adopting grey relation analysis method we will optimize the bits which suit the stratum. The method overcome the defects of the neural net method of modeling difficulty and identifying confused, which has the merits of speedy, intuition, simply and high coincidence rate.Based on the crustal stress test, the crustal stress direction and value using logging information were developed and the crustal stress section was established. From researching we founded that the crustal stress valve showsσ_V >σ_H >σ_h and theσ_H direction is W-E. Whereas the stratum abnormal high pressure character in Xu Jia-he of Chuan-xi area and the limitations of predicting stratum using equivalent depth method, adopting the model between interval velocity and effective stress based on the theorem of effective calculate the pore pressure. At the same time using predecessors' empirical formula combining the engineering geology character of Chuan-xi, optimize the logging calculation models about stratum caving pressure and break down pressure which suit work place, we will obtain the safe drill fluid density window which will prevent the destabilizing of the wall of a well. The examples manifest that the stress, the three stratum pressures and the drill mud density window are reasonable, and satisfy the need of fact drilling engineering in local.The stratum in Xu Jia-he of Chuan-xi has the traits of low porosity, low permeability, poor drillability and strong abrasivity etc. Adopting under Balanced Drilling will favor to protect hydrocarbon reservoir, remove chip hold down effect to raise the drill speed, avoid drill fluid leaking and differential pressure sticking accidents etc. Using Under Balance Logging will obtain stratigraphic information on time. This text based on the measure theory of acoustic logging, electric logging and nuclear logging offered the selection of wireline logging series in gas filled medium under the UBL condition and analyze the character of logging curve response and abnormal phenomena under UBL condition, which form a method on reservoir parameter under UBL condition. The effect is better.