Identification Of Abnormal High Pressure Gas Reservoir In

The lithology of Longnvsi structure in Sichuan Basin is mainly composed of carbonate rocks,its complex geological structure,fault,and fracture developed,the pressure coefficient ranges from1.0to1.9,obviously it is abnormal high pressure layer.This paper takes Shaxi Temple to Dengying group as the main research object,makes full use of geological data,drilling data,logging data and so on,starting from the angle of rock mechanics,focusing on the prediction of pore pressure and the methods of identification gas layer,and provides a theoretical basis and reference for the development and drilling of high pressure gas reservoir.The main researchs and results are as follows:(1)Based on the framwork of NCRA method,the complex lithology analysis was carried out,the content and porosity of each layer were counted out,and the lithology profile of the work area is established.Utilizing FMI analysis the structural characteristics of the target layer cracks and holes and other void spaces. This provides a basis for lithology and physical properties to identify abnormally high pressure gas reservoir.(2) When calculating the formation pore pressure,the methods of conventional calculation ignored the factors such as the expansion of fluid,tectonic compression and so on,the calculation accuracy of the formation pore pressure was reduced.The main causes of Longnvsi structure is the formation of abnormal high pressure unload effects,including hydrocarbon source rock oil generation and oil crack to gas.This paper chooses the improved Eaton method and the effective stress method to calculate the formation pore pressure of the sand shale and carbonate formation separately.The calculation results are in conformity with the actual,it turned out abnormal high pressure in Daanzai to Qiongzhusi group.(3)Using horizontal and vertical wave differential of the key layers,getting the calculation formula of horizontal wave by the means of regression,building a horizontal wave differential curve without array acoustic wave data based on that formula.To provides rock mechanics parameters for the calculation an important basis for the data.(4)Based on the acoustic characteristics of gas bearing stratum theory,high pressure gas reservoir has a relatively low PR, CB is relatively large,CMCF is much larger than the non-gas reservoir and other rock mechanics characteristics.Calculating the rock mechanics sensitive parameters accurately by using AC curve and DEN curve,with the testing results as the reference standard,the chart of gas layer identification was established by using intersection method of two parameters in different block and geological layer,the interpretation standards of gas and water layer was determined according to the identification chart.(5)Gray correlation analysis took into account the gas reservoir response characteristics that reflect a variety of parameters,intuitive and convenient advantages.The fluid types of research area center layer were established by adopting rock mechanics parametersand four parameters,six parameters separately. Based on which the fluid type of the layer was identified.Work area using the above three methods to identify key wells reservoir fluid type,the highest compliance rate is rock mechanics parameters Gray Relation.(6)Combined drilling and logging data work area to identify abnormally high pressure gas reservoir in each well,high pressure gas reservoir drilling technology has its corresponding measures,it should be avoided kick,blowout accident occurred in the complex process of drilling a high pressure gas reservoir.With the series of methods and models mentioned above,the analysis of complex lithology,the parameters of rock mechanics,the calculation of formation pressure calculation and the identification of gas layer has been set and it has good effect,which provides an effective evidence for the recognition of abnormal high pressure gas reservoir and drilling and development.