The Study On In-situ Stress Of Loose Sandstone Reservoir In Offshore Oilfields

As the pelitic unconsolidated sandstone reservoir in offshore oilfields has a high contentof pelite which needs to be exploited through the fracturing production now, mechanicalParameters of the oil reservoir as well as in-situ stress shall first be determined in order tostudy the effects of hydraulic fracturing. Then the fracturing simulation can be made in orderto study the effects of hydraulic fracturing.This paper did the existing ground stress calculation model comparison and selected theoptimal one for loose sand. Based on the experimental rock mechanics parameters of the core,combined with field logging data and the in-situ stress calculation model, the research got theprofile of rock mechanics parameters and the in-situ stress state of loose sandstone reservoirin offshore oilfields; then the calculation results were analyzed. In addition, the in-situ stresscalculation software considering all of the current calculation patterns of in-situ stress wasbuilt. The empirical formula can be manually entered in the software, which greatly improvedthe practicability and application scope of the software.Given that some well is lack of acoustic logging data, this paper proposed a way of usingdrilling parameters to predict wave velocity for further prediction of in-situ stress. Themathematical model that predicts wave velocity by using the drilling parameters is suggested,and further analysis about the applicability of the model is given. Combined with the depth-density relationship fitted, in-situ stress can be calculated in the last. Field application provesthat the prediction accuracy of the model is higher and this model is a feasible method topredict wave velocity. In order to simplify the calculation process of predicting vertical wavevelocity, the software which can use drilling data to calculate wave velocity and draw thewave velocity curve is compiled.