ABSTRACT

Horizontal drilling has been applied in tight-gas reservoirs to enhance drainage and, when combined with fracturing stimulation, often results in a high-productivity well. Throughout the last several years, developments in openhole horizontal completions have been designed to stimulate the entire horizontal interval by segmenting the well with mechanical devices, such as compression set packers and chemical swelling packers. The advanced completion system with a series of mechanical openhole packers was designed to generate hydraulic fractures in each desired interval while the mechanical packers provide mechanical diversion at high differential pressures. This paper examines the hydraulic fracturing process under the influence of packers under in-situ stress conditions. Boundary element analysis incorporating the fiction stress method (FSM) and the displacement discontinuity method (DDM) is preformed to simulate the fracturing process. The boundary element method (BEM) is used because it does not require any artificial boundaries for unbounded problems and is well-suited for modeling fractures. Stress distributions around transverse fractures are investigated to understand the influence of existing fractures. The results indicate that the sealing pressure of the open hole packers against the borehole must be carefully selected to avoid generating unwanted fractures along edges of the packers.

1. INTRODUCTION

The number of horizontal wells drilled has increased significantly in the past decade, along with more technical developments in horizontal completion methods and fracturing stimulation in unconventional, low-permeability reservoirs. Early techniques, such as the use of limited entry and bullheading, provide little improvement compared to vertical wells. Throughout the last several years, developments in openhole horizontal completions have been designed to stimulate the entire horizontal interval by segmenting the well with mechanical devices, such as compression set packers and chemical swelling packers. Two techniques have proven successful at creating transverse fractures in horizontal wells. In cemented and cased horizontal wells, if the wells are drilled in the direction of the minimum stress and then perforated with short intervals (no more than four times the openhole diameter of the wellbore), a transverse planar fracture will be generated. In openhole horizontal wells, hydrajet perforating is necessary to create a clean, non-damaged, fairly large and continuous path through the borehole wall into the formation [1]. The eroded tunnel should be created along the maximum horizontal in-situ stress and will help initiate transverse fractures in either a normal or strike slip stress regime. An advanced completion system with a series of mechanical openhole packers to generate fractures in each desired interval is studied using the BEM. Boundary element analysis incorporating the FSM and DDM are performed to simulate transverse fractures initiated from horizontal wellbores. The BEM is used because it does not require any artificial boundaries for unbounded problems and is well-suited for modeling fractures. Previous works in literature primarily study stress distributions around the wellbore wall and tangential stress distribution along the packer-influenced zone caused by different packer pressures throughout formations [2, 3]. There is a lack of analysis on the axial stress distribution along the wellbore and influence of generated fractures on the subsequent fracturing stage.

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