The Importance of In-Situ-Stress Profiles in Hydraulic-Fracturing Applications
- C.W. Hopkins (S.A. Holditch & Assocs. Inc.)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- September 1997
- Document Type
- Journal Paper
- 944 - 948
- 1997. Society of Petroleum Engineers
- 2 Well Completion, 5.8.2 Shale Gas, 7.1.10 Field Economic Analysis, 1.13.1 Casing Design, , 1.13 Casing and Cementing, 5.8.1 Tight Gas, 5.6.1 Open hole/cased hole log analysis, 2.1.3 Sand/Solids Control, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 3 Production and Well Operations, 2.4.1 Fracture design and containment, 2.1.1 Perforating, 5.4.2 Gas Injection Methods, 5.5.8 History Matching, 7.1.9 Project Economic Analysis, 4.1.2 Separation and Treating, 1.6 Drilling Operations, 5.5 Reservoir Simulation
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Technology Today Series articles provide useful summary informationon both classic and emerging concepts in petroleum engineering. Purpose: Toprovide the general reader with a basic understanding of a significant concept,technique, or development within a specific area of technology.
In-situ stresses define the local forces acting on lithologic layers in thesubsurface. Knowledge of these stresses is important in drilling,wellbore-stability, and, especially, hydraulic-fracturing applications. Themeasurement of in-situ stress is not straightforward and, therefore, often goesunmeasured. As such, we often assume values of in-situ stress or estimatein-situ stresses from logging parameters. This article illustrates theimportance of in-situ-stress estimates as they relate to hydraulic fracturingand outlines several techniques for estimating in-situ-stress magnitudes.
The in-situ stresses acting on a formation can be decomposed into threeprincipal compressive stresses, one vertical and two horizontal. The twohorizontal compressive stresses are usually not equal. The vertical stress iscaused by the overburden weight acting on the top of a formation. Thehorizontal stresses are the result of the poroelastic deformation of the rocksplus externally applied tectonic forces. The parameters that affect themagnitude of the in-situ stresses include overburden weight, fluid porepressure, porosity, anomalies in the rock fabric (i.e., natural fractures),rock mechanical properties (such as Poisson's ratio), and tectonicactivity.
Knowledge of the in-situ-stress magnitude and direction can impact decisionsand designs throughout the drilling and completion of a well. During drilling,in-situ stress may affect the mud and cement densities required to preventunwanted fracturing of openhole strata in the wellbore. For wells that will bestimulated at high pressures, casing design must account for the maximumanticipated stresses. Wellbore-stability calculations, particularly forhorizontal wells, require knowledge of in-situ-stress magnitude anddirection.
For hydraulic-fracture treatment applications, the in-situ stresses controlfracture azimuth and orientation (vertical and horizontal), fracture-heightgrowth, fracture width, treatment pressures, and fracture conductivity. As Fig.1 illustrates, fractures grow perpendicular to the minimum in-situ-stressdirection; thus, stress direction can affect well-placement and -spacingdecisions.
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