Genetic Mechanism and Evolution of the Covert Fault Zone and Its Oil-Controlling Mode in Qikou Sag, Eastern China

Abstract

Covert fault zone is an important type of geological phenomenon that is closely related to hydrocarbon formation and distribution but has often been overlooked because it lacks obvious fault displacement and fault plane. To meet this challenge, a novel cognitive framework is proposed in this study, in which criteria for identifying the existence of covert fault zone are developed based on the regional tectonic backgrounds and geophysical data. The Riedel shear model is then utilized to analyze the genetic mechanism of the covert fault zone. The Mohr-Coulomb theory is also introduced to conduct a structural physical simulation to interpret the evolution process of the covert fault zone. Information about the genetic mechanism and evolution of the covert fault zone is finally combined to determine the oil-controlling mode. The study site is Qikou Sag in Eastern China. It is found that the covert fault zone in Qikou Sag meets four recognition criteria and is generated by the stress transferred from the strike-slip activity of the basement fault. Moreover, it can be concluded that the covert fault zone in Qikou Sag contains five evolution stages and controls the reservoir mainly via three aspects, that is, sedimentary sand, subtle traps and oil accumulation mode.

Effects Evaluation on Multiround Injection of a N2 Foam & Viscosity Reducer to Improve the Recovery of Fault-Block Heavy Oil Reservoir with Edge-Bottom Water: A Two-Dimensional Visualization Experimental Study

“…3 We recorded the foam volume in the foam evaluation device and measured the drainage half-life of the foam. 4 We changed the mass concentration of the foaming agent solution and repeated the experiment.…”

“…However, in the later stage of production, after a significant decrease in pressure within the reservoir, the edge and bottom water will rush forward, limiting the swept range of water flooding and causing a rapid reduce in oil production . Fault-block reservoirs are often characterized by a small scale and small oil-bearing area, but they have good sealing properties and irregular shapes . The injection-production systems are usually incomplete, which prevent the formation of regular well patterns .…”

“…3 Fault-block reservoirs are often characterized by a small scale and small oil-bearing area, but they have good sealing properties and irregular shapes. 4 The injectionproduction systems are usually incomplete, which prevent the formation of regular well patterns. 5 As a result, water flooding has limited effectiveness in these reservoirs, exacerbating the problem of exploitation.…”

A Novel Assisted Gas–Oil Countercurrent EOR Technique for Attic Oil in Fault-Block Reservoirs

“…Baker et al [26] used the gas-oil ratio interpolation map of different production wells to evaluate the gas-oil segregation and the formation of a secondary gas cap in Pine Creek Cardium oil field at Alberta, Canada. In this work, the length of different phases is measured and the fraction of different phases in the sampling tube is calculated by Equation (1). According to the drawing method of the interpolation map, the distribution of a specific phase could be obtained.…”

“…Fault-block reservoirs are widely distributed in eastern China and the reservoir characteristics are generally expressed in terms of the large dip angle, small oil-bearing area, good sealing ability, and complex fault structure [1][2][3][4]. In order to ensure the fault sealing ability, the production well is generally drilled 50-80 m away from the top fault boundary [5,6].…”