Chemical Thermodynamics Prediction Methods Of Secondary Porosity In Sedimentary Basin

Secondary porosity is the pores which formed of particulate,host or cementing matter affected by solution or dissolution during diagenetic process. Secondary porosity of diagenetic process is extremely complicated, diagenetic system often simultaneously with multiple diagenetic reaction, and these reactions are interacted and restrainted for each ather.This paper summarizes a large number of conclusion of secondary pore causes and influencing factors in domestic and foreign, further discussed the causes of secondary porosity in the middle and shallow of northern songliao basin, we consider that the main reasons of the formation of secondary porosity in this area are the dissolution of feldspar. Through analyzing the mechanism of feldspar dissolution, we consider that organic acid is the main control factor of feldspar dissolved, organic acid determines the development status of secondary porosity zone, organic acid accumulative total yield high region is the favorable development zone of secondary porosity.Through comparing the reaction business of feldspar dissolution reaction in present formation water and the equilibrium constant calculated by thermodynamic method, we confirmed the feldspar dissolution reaction in major stratum space of study area is in equilibrium or nearly in equilibrium. The reaction business of feldspar dissolution reaction is changed by the acid, the original business of the dissolution reaction is destroyed, the reaction establish a new equilibrium after equilibrium shifting, and this is the process of formation of secondary porosity. The development degree of secondary porosity is proportional to the effect of the acid to the reservoir. Based on the chemical dynamics method of calculating the amount of effective acid produced by mudstone pyrolysis, this paper established a method to calculate the cumulative amount of acid work on the reservoir, and a method to predict the Spatial distribution of second porosity growing status.We chose a E-W section SL1 and a N-S section SL2 in the north Songliao basin, according to the reservoir the vertical division, according to the structure in horizontal division, predicted the growing status of secondary porosity zone with the above miniature. The prediction results show that, in the vertical, the highest acid effect index in each region appeared is in Gaotaizi oil layer, secondly in Saertu oil layer and Putaohua oil layer, thirdly in Heidimiao oil layer and Fuyu oil layer, the lowest is in Yangdachengzi oil layer; In the EW structure, the secondary porosity best growing in Daqing Changyuan, secondly in Sanzhao sag and Qijia-Gulong sag, poorer growing in Chaoyanggou terraces and Dongnan uplift. Inside of Qijia-Gulong sag, the south area is better than the north area in Saertu oil layer and Gaotaizi oil layer, north and south is not very different in Heidimiao oil layer and Putaohua oil layer, north is little better than south in Yangdachengzi oil layer. The secondary porosity general growth in north plunge area.