The Evolutional Characteristics and Quantitative Prediction of Tight Oil Saturation: Evidence from Physical Modeling of Oil Charging in Tight Reservoirs And X-ct Screening

Abstract

To study the evolutional characteristics and quantitative prediction of tight oil saturation, 16 tight sandstone core samples from the Permian Lucaogou Formation (LCG) in Jimsar Depression of Eastern Junggar Basin were selected for physical modeling of oil charging and X-CT screening. The increasing of tight oil saturation can be divided into four stages, i.e. initial increasing stage(A), rapid increasing stage(B), slow increasing stage(C) and stable stage(D). During the stage A, the increases of oil saturation is less than 5%, while in the stages C and D the values are 6%~14% and less than 3%,respectively. The maximum increases (about 26%~52%) of oil saturation was in the stage B, and linear or exponential relationship between oil saturation and charging dynamics can be established. The pressure gradient, reservoir and fluid properties are the main factors which control oil saturation increasing in tight sandstone. Positive correlation relationship between oil saturation and pressure gradient and permeability can be determined, while negative with oil viscosity. Based on the fitting function between oil saturation and pressure gradient, permeability and oil viscosity, the quantitative predictive graph of tight oil saturation was built. The charging pressure gradient in LCG formation varied from 11MPa/km to 48MPa/km, the permeability under overburden pressure varied in the range of 0.01~0.12mD, and the average oil viscosity is 52 mPas. Based on the data and graph, tight oil saturation in LCG was calculated in the range of 38%~73%, which is similar to the measured oil saturation (35%~82%) in laboratory. This study could provide a new method for predicting tight oil saturation and significant mechanism of hydrocarbon accumulation in tight reservoirs.

AAPG Datapages/Search and Discovery Article #90332 © 2018 AAPG International Conference and Exhibition, Cape Town, South Africa, November 4-11, 2018