Multi-Stage Fracturing and Production Induced Stress Field Simulation

Wei, Shiming (State Key Laboratory of Petroleum Resources and Prospecting / China University of Petroleum) | Chen, Mian (State Key Laboratory of Petroleum Resources and Prospecting / China University of Petroleum) | Jin, Yan (State Key Laboratory of Petroleum Resources and Prospecting / China University of Petroleum) | Lu, Yunhu (State Key Laboratory of Petroleum Resources and Prospecting / China University of Petroleum) | Xia, Yang (State Key Laboratory of Petroleum Resources and Prospecting / China University of Petroleum)

OnePetro 

Abstract

The carbonate reservoirs in western China have low porosity, low permeability and high heterogeneity, thus multi-stage acid fracturing is usually implemented, and refracturing is also needed. During the procedure of multi-stage acid fracturing, interactions among artificial cracks must be cleared, which are also called stress shadows and related to the success of multi-level fracturing measures. The production of multi-stage fracturing well always reduced rapidly, thus the refracturing procedure is carried out. However, As the well has been produced for some time, the stress field around the wellbore has changed. And we have to design the refracturing scheme according to the new stress field. Using the boundary element method to calculate the crack propagation induced stress field in the multi-stage acid pressure process, we can determine the size of the stress shadow, and whether the subsequent crack can be cracked. Using finite element method based on the poroelastic theory, we can get the production induced stress field. Before that, reservoir’s geometrical model was built with DNF (discrete natural fractures), employing crack propagation simulation results to get the artificial crack parameters, using the logging and seismic data to get characteristics of the natural fracture distribution, and determining the type of natural fractures that artificial cracks link to with the fracturing construction curve. After the construction of reservoir’s geometrical model and before the simulation of production induced stress field, the accuracy of the model is verified using some wells’ production data.

1. Introduction

The Carbonate reservoir has been found to dominate the proved reserves in western China, which is an important area for Chinese petroleum production increase. The refracturing technique is an important approach to raise the production of Carbonate reservoirs, which are strongly characterized by low porosity and permeability of matrix wherein a large number of natural fractures is well-developed. Theses carbonate reservoirs gave high outputs after being acid fractured, however, the high flow rate could not last long. Therefore, the refracturing is needed. When we design the fracturing and refracturing, current stress fields are an important reference. And the key technical problem is to calculate the induced stress during fracturing and production process together and accurately.