Origin And Quantitative Prediction Of Abnormal Pressure In Deep Formation, Northeast Sichuan, China

In complex exploration area in Northeast,due to multi-tectonic movement,resulted in deep dense carbonate rock strata exists high pressure,it is directly related to drilling, personal and property security, resulting in exploration difficult. To solve the problem of deep carbonate formation pore pressure calculation in northeast region, integrated with geological, geophysical, analysis and test, using petroleum geology, drilling technology guidance, studying on the geological model, the pressure distribution gas reservoir characteristics, pore and crack formation mechanism of gas reservoir pressure, pressure prediction, and on-site monitoring ,we do a system analysis and a quantitative analysis on pressure mechanism in Puguang and Mao dam area of the Northeast Sichuan .Study the geological modeling under the background of pressure,discuss the relationship between sedimentation model and distribution of formation pressure: it is considered that the development of special reservoir strata controlled by sedimentary facies from marine carbonate formation has an important effect on the distribution of pressure,the paper has distinguished the different characteristics of pressure between porous gas pools and fractured gas pools. Porous gas pools of platform edge shallow facies show the"normal pressure", continental shelf and open platform have mainly developed in fractured gas pools ,and show"excess pressure". Using the methods of geology ,computer simulation for the pressure in the study area, establish a three-dimensional space distribution of stress, and the simulation results compared with the measured pressure data, the trend consistent.The formation mechanism of Carbonatite's overpressure is very complicated. Strata pressure is caused by hydrocarbon cracking and tectonic compression that is mainly cumulative stress. Because of depositional setting, rock types, and different physical characteristics and effect of thermo chemical sulfate reduction(TSR), variety of roles mix to control today's pressure characteristics.It has studied that crude oil cracked gas to increase strata pressure obviously and caused high pressure. Specific to the puguang area, existing pressure relief mechanism such as thermochemical sulfate reduction, tectonic uplift and so on , Thus forming atmospheric pressure. While high pressure and overpressure is caused by strong tectonic compression in late stage of Yanshan and Himalayan in Mao dam area,and reservoir mainly developed for the fractured reservoir limestone (dolomite) , because of strong self-enclosed of fracture,overpressure will not release easily,so this is the main factor which caused high pressure of deep reservoir in mao dam area.On the base of sedimentary background and causes of abnormal pressure analysis, it is known that the effective stress is able to reflect the changes of carbonate formation rock pore pressure. This depends on Vertical and horizontal velocity ratio and effective stress of high-index, and we do a helpful discuss related to design procedure for deep pore pressure prediction.Deep stratum of not-proven formation conditions pressure calculation result often cannot meet the engineering application due to seismic resolution , so the pressure with monitor drilling is particularly important.In this paper , the equation is based on the concept of broken rock and definition of rock drillability value, combined with the level of indoor experiment data and considering influnce of the effective mouth power of the bit and differential pressure on the penetration rate.