Abstract

The optimum fracturing design of a systematic fracturing reservoir is based on the comprehensive simulation of propped fractures and the fractured reservoir. On the basis of postfrac characteristics of fluid flow in the naturally fractured low-permeability reservoirs, a new mathematical model of fluid flow in porous media including matrix, natural fractures and propped fractures has presented in this paper. The influence of non-Darcy flow in the propped fracture and the fracture permeability sensitivity of net stress were taken into account in the model. The fully implicit numerical model was derived and a fracturing reservoir simulator was first developed. According to the simulation results, the effects of the parameters associated with natural fractures or propped fractures and well patterns on psotfrac production performance in the naturally fractured reservoirs in northwestern china were synthetically analyzed. The design principles of fracturing reservoir technique in this reservoir were outlined and the stimulation effectiveness in the condition of different fracturing operations was investigated. The simulation results were provided for working out the plan of systematic fracturing reservoir treatment. The application of this plan to this reservoir has successfully solved the contradiction of the investment and production. The systematic fracturing technique improved the well productivity and satisfied the demand for the recovery rate.

Introduction

Hydraulic fracturing technique, intersecting and infiltrating with other subjects, has developed from the common well stimulation into the systematic fracturing technique in the low permeability reservoir. The theoretical researchers and stimulation engineers have been paying highly attention to fracturing technique in the naturally fractured reservoirs and have performed a series of investigations and treatments in recent years. Based on the comprehensive application of the hydraulic fracture simulation and simulation of the reservoir with propped fractures, the effectiveness evaluation of systematic fracturing in the naturally fractured and low permeability reservoir is the fundamental of the optimization design of systematic fracturing treatment.

The prediction and evaluation methodologies of fractured well production performance are summarized as three kinds of methods: one is the method of calculating fractured well productivity, another is modern mach method of typical curves, the third is numerical simulation method. The Prats method and the Mcguire- Sikora method are the typical methods of calculating fractured well productivity. This method is very simple and so it is easy to be acceptable and popularized for the fracturing engineers in the oil fields. According to the methodology of matching typical curves in well testing, the pressure and production performance of fractured wells can be obtained. The main typical curves are those curves presented by Holditch S.A. or Cinco-Ley or Agarwal. This method is mainly used in a single fractured well. The numerical simulation technology is used to simulate the production performance either in a single fractured well or in a systematic fracturing reservoir. The performance simulation for a single fractured well has been employed in the fracturing optimization design and fracturing economic analysis very well. At present the main objective of the study focuses on the simulation of the fracturing reservoir.

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