Abstract
Aimed at ultra-low permeability reservoirs, the recovery effect of inverted nine-spot equilateral well pattern is studied through large-scale natural sandstone flat model experiments. Two adjustment schemes were proposed based on the original well pattern. This essay has put forward the concept of pressure sweep efficiency for evaluating the driving efficiency. Pressure gradient fields under different drawdown pressure were measured. Seepage area of the model was divided into immobilized area, nonlinear seepage area and quasi-linear seepage area combining with the nonlinear seepage experiment of the small twin core. The results showed that the ultra-low permeability sandstone flat model was characterized as nonlinear seepage law and threshold pressure gradient obviously. For one quarter of the inverted nine-spot equilateral well pattern, the middle region is difficult to develop. The recovery effect can be improved by adjusting production wells or adding injection wells. And the best solution is transforming the corner production well into injection well.
Highlights
The investigation of the well patterns is one important aspects of an oil and gas field development which is a complex and systemic engineering
Some researchers studied through artificial sand filling model experiments (Geertsma et al, 1956; Gaucher and Lindley, 1960; Craig et al, 1957; Rapoprt, 1995; Butler, 1987; Sugianto and Butler, 1990; Zhou and Wang, 1994; Shen et al, 2004; Wang et al, 2005)
Physical model preparation: Quotation (Xue et al, 2011; Xu et al, 2012): By constant-rate mercury injection, when porosity and permeability of the natural sandstone outcrops are close to those of the ultra-Low Permeability Reservoir, their throat radiuses are similar to each other. This proves that natural sandstone outcrops can be used to simulate the ultra-low permeability reservoir in the experiments
Summary
The investigation of the well patterns is one important aspects of an oil and gas field development which is a complex and systemic engineering. The effects of many factors on waterflooding in ultra-low permeability oil field, such as the stronger heterogeneity of reservoirs, the bigger threshold pressure difference and driving pressure gradient, the natural fracture development and the declining productivity index after water breakthrough are getting increasingly strong (Li et al, 2002). Most of the researchers studied well patterns through theoretical analysis, field testing and numerical simulation (Muskat, 1946; Tong, 1983; Zhang et al, 2000; Hou et al, 2000). This research enriches the well pattern research methods, and provides theoretical basis for effective development of ultra-low permeability reservoirs
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