Abstract

Horizontal well hydraulic fracturing can help develop unconventional petroleum resources using techniques such as simultaneous and sequential fracturing. To achieve successful and desired stimulated rock volumes and fracture networks, it is beneficial to understand the effect of fracture spacing and various rock and fluid properties on stimulation to minimize the risk of unwanted fracture geometries. This paper investigates the effectiveness of fracturing techniques using a fully coupled 2D plane strain numerical model based on displacement discontinuity method [1]. The multi-stage fracturing model considers different boundary conditions for the previous stage fractures, such as constant pressure restricting the flow back between stages and proppant-filled. A series of examples are presented to demonstrate the effect of fracture spacing on resulting fracture system geometry and stimulated rock volume. The model is also used to compare the conventional zipper fracturing technique (i.e. fracturing multiple parallel horizontal wells sequentially) with modified zipper fracturing technique. The results highlight the fracture apertures and geometries to achieve optimization of fracturing process. The paper also discusses the effects of rock anisotropic characteristics of shale on the fracturing results

1. INTRODUCTION

Increased interest in exploration and production of lower grade reservoirs presents new challenges in design and evaluation of hydraulic stimulation treatment of horizontal wells. Each treatment stage in a well is designed to stimulate a reservoir volume to create a desired permeability enhancement. The collective stimulated zones should affect the maximum volume with minimal overlap of adjacent treatment stages. Usually, fracturing treatment of horizontal wells is carried out using one of two schemes namely, Simul- Frac and Sequel-Frac. In simultaneous fracturing multiple fractures are created and propagated at same time whereas in sequential fracturing, fractures are created one after another usually by keeping the previously created fracture/fractures either propped or pressurized with fluid. Zipper fracturing is a technique where two or more lateral horizontal wells (usually at the same depth) are fractured simultaneously or sequentially [2]. The main purpose of zipper fracturing is to create close fractures and maximize stimulation effect, thus improving the stimulated rock volume. In all cases, the perforation clusters should be placed such that competing stress-shadow effects between them is minimized. By reducing the number of clusters per stage, costs are reduced and stress interference is minimized, reducing the possibility of having ineffective fracturing.

This content is only available via PDF.
You can access this article if you purchase or spend a download.