Abstract:

Heterogeneity in geomechanical conditions likely contributes to the observed variability in hydraulic fracturing treatment performance. We propose a methodology to assess fracturing performance and risks based on geomechanical conditions. High-level indicators include completion integrity, horsepower efficiency, reservoir exposure, fracture containment, and connectivity aspects, which are each broken down into a tree-like structure of contributing sub-factors, to the point where they can be related to geomechanics-based drivers. These drivers are derived from 3D geomechanical models and used to identify in 3D space where the conditions appear to be more or less favorable from a fracturing standpoint. The results can be used to identify where chances of success are higher. Applications range from pilot well location in a newly explored area to well positioning and landing during development, to completion design (when model resolution permits). Identified risks, if any, also inform completion design to mitigate these risks. A field case example is used for illustration purposes.

Introduction

Hydraulic fracturing treatments are not all equally successful. Whether measured by treatment data (e.g., amount of proppant placed) or by production data, fracturing often exhibits variable performance across stages along a well, or between wells within a field. For example, certain formations may prove difficult, if not impossible to breakdown; high screen-out rates may occur; and certain stages may dominate production, while others contribute very little (Miller et al., 2011). The above holds true across stages designed and executed similarly, if not identically, which clearly indicates that the subsurface has a primary control on the outcome.

Subsurface controls are generally split between Reservoir quality, or RQ, and Completion Quality, or CQ (Cipolla et al., 2011). RQ refers to the resource itself and is assessed based on indicators such as reserves and producible reserves. CQ refers to the effectiveness of reservoir stimulation by hydraulic fracturing. Importantly, the former is a given whereas CQ can, to a certain extent, be engineered. Therefore, RQ is pre-requisite to CQ.

Hydraulic fracturing treatments across zones with similar RQ often exhibit widely different production performance. Such is the case in relatively thick shale plays (many hundreds of feet), where, by experience, the wellbore landing targets have been narrowed down to 10-20 ft. Some of this variability is caused by heterogeneity in CQ. It is reasonable to assume that geomechanical conditions, including rock fabric and stresses, are key ingredients of CQ. Geomechanical conditions broadly affect the hydraulic fracturing process. In particular, they exert a primary control on fracture geometry (Economides & Nolte, 2000): the orientation of the minimum stress direction strongly influences the direction of fracture propagation, variations in stress and mechanical properties between layers control fracture height growth and fracture width and even the possible development of pinchpoints, all of which strongly influence the final hydraulic fracture geometry, the placement of the proppant, and how the newly created reservoir contact surface connects to the wellbore and delivers production performance.

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