The Study On Pore Pressure Prediction In Marine Carbonate Rock Formation

Marine carbonate sequences are national current and future petroleum resources vital succeed zone, which are in buried deep stratum, developed pores, cracks, holes, whose structure is complicated. Predicting the abnormal pressure can be contained two aspects:before drilling and drilling. The former mainly relied on seismic technology, which is suit for lower levels of exploration area, but because of depth, igneous, and the shielding effect of the impact of salt-gypsum rock, resulting in poor quality seismic data, the low prediction accuracy. At higher levels of exploration areas, pressure data is measured by the statistical analysis of the pressure data or create a three-dimensional system to accurately predict. Drilling forecast mainly rely on logging-while-drilling technology. Because of clastic sedimentary formations with continuous compaction, according uncompacting principle by seismic velocity, dc index data for pore pressure prediction. The chemical cementation of carbonate rocks larger than mechanical compaction, which causes abnormal high pressure mechanism and prediction methods are different from clastic strata, and thus more difficult. Carbonate rocks abnormally high pressure prediction is truly world-class problem. If the pore pressure cannot be accurately predicted, drilling completion engineering design and construction will be lack of effective basic parameters, which may lead to the construction of the complex failure, and even accidents, can greatly restrict the exploration of oil and gas resources in marine carbonate rocks development process.Based on the understanding of relevant theoretical background, research status and development trend basis, combined the characteristics of marine carbonate rocks in northeastern Sichuan, which can easy to generate abnormally high pressure gas reservoir, abnormally high pressure gas reservoir can be recognized and predicted by the marine carbonate laws of acoustic characteristics.The study includes four parts, the first part of the analysis of marine carbonate causes abnormal pressure mechanism. By analyzing the relevant information, to get an abnormal high pressure pyrolysis mechanism supercharging liquid hydrocarbons, filling the role of natural gas booster bottom, keeping the role of tectonic compression and capping of high supercharging pressure. The pressure drop of cooling mechanisms contains uplift and erosion of decompression, relief role TSR reaction and tectonic uplift antihypertensive effect.The second parts of the longitudinal wave on marine carbonate rocks were derived. P-wave velocity obtained by rock skeleton and pore fluid velocity speed items composed; the speed of skeleton depends on the entry lithology and pore structure, which determines the compressional wave velocity trends, and pore fluid speed depends on the size of the pore pressure of the rock, which decided P-wave velocity slight fluctuations. Finally theoretically derived from the contribution of the pore fluid velocity of longitudinal waves can be positive, negative or zero.The third part is the experiment demonstrated by relevant factors rock wave velocity amplitude fluctuations arise mainly from small size, pore fluid pressure in the rock pores of rock wave velocity contribution can be positive, negative and zero. The critical pressure can be calculated pore fluid compressional wave velocity of rock whether positive or negative. It provides a theoretical and experimental support to predict pore pressure of marine carbonate formation using acoustic characteristics.The last part is the field application of research and demonstration part. Sound waves law characteristics can be used to identify the depth of abnormally high pressure gas reservoir, as well as predict the abnormally high pressure are above the critical pressure, and finally according to the relevant well history data and the measured pressure data of each well can demonstrate the accuracy of abnormal high pressure is predicted by using the acoustic characteristics. It provides a certain reference value for the pore pressure prediction model of marine carbonate rocks.