The Importance of In-Situ-Stress Profiles in Hydraulic-Fracturing Applications

It is very important to study the pristine stress field in Civil, Mining, Petroleum engineering as well as in Geology, Geophysics, and Seismology. There are various methods of determination of in-situ stress in rock mass. However, hydraulic fracturing techniques is the most convenient method to determine and interpret the test results. Based on an hydraulic fracturing stress measurement campaign at an underground liquefied petroleum gas storage project which locates in ZhuHai, China, this paper briefly describes the various uses of stress measurement, details of hydraulic fracturing test system, test procedure adopted and the concept of hydraulic fracturing in arriving at the in-situ stresses of the rock mass.

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Apparent Toughness Anisotropy Induced by “Roughness” of In-Situ Stress: A Mechanism That Hinders Vertical Growth of Hydraulic Fractures and Its Simplified Modeling

SPE Journal ◽

10.2118/194359-pa ◽

2019 ◽

Vol 24 (05) ◽

pp. 2148-2162 ◽

Cited By ~ 2

Author(s):

Pengcheng Fu ◽

Jixiang Huang ◽

Randolph R. Settgast ◽

Joseph P. Morris ◽

Frederick J. Ryerson

Keyword(s):

Hydraulic Fracture ◽

High Stress ◽

In Situ Stress ◽

Height Growth ◽

Hydraulic Fractures ◽

Simple Relationship ◽

Vertical Growth ◽

Stress Profiles ◽

Fracture Height

Summary The height growth of a hydraulic fracture is known to be affected by many factors that are related to the layered structure of sedimentary rocks. Although these factors are often used to qualitatively explain why hydraulic fractures usually have well–bounded height growth, most of them cannot be directly and quantitatively characterized for a given reservoir to enable a priori prediction of fracture–height growth. In this work, we study the role of the “roughness” of in–situ–stress profiles, in particular alternating low and high stress among rock layers, in determining the tendency of a hydraulic fracture to propagate horizontally vs. vertically. We found that a hydraulic fracture propagates horizontally in low–stress layers ahead of neighboring high–stress layers. Under such a configuration, a fracture–mechanics principle dictates that the net pressure required for horizontal growth of high–stress layers within the current fracture height is significantly lower than that required for additional vertical growth across rock layers. Without explicit consideration of the stress–roughness profile, the system behaves as if the rock is tougher against vertical propagation than it is against horizontal fracture propagation. We developed a simple relationship between the apparent differential rock toughness and characteristics of the stress roughness that induce equivalent overall fracture shapes. This relationship enables existing hydraulic–fracture models to represent the effects of rough in–situ stress on fracture growth without directly representing the fine–resolution rough–stress profiles.

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In situ stress determination by hydraulic fracturing—a method employing an artificial notch

International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts ◽

10.1016/0148-9062(89)91969-4 ◽

1989 ◽

Vol 26 (3-4) ◽

pp. 197-202 ◽

Cited By ~ 10

Author(s):

K. Hayashi ◽

T. Ito ◽

H. Abe

Keyword(s):

Hydraulic Fracturing ◽

In Situ Stress ◽

Stress Determination

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Fracturing curve and its corresponding gas productivity of coalbed methane wells in the Zhengzhuang block, southern Qinshui Basin, North China

Energy Exploration & Exploitation ◽

10.1177/0144598720923820 ◽

2020 ◽

Vol 38 (5) ◽

pp. 1387-1408

Author(s):

Yang Chen ◽

Dameng Liu ◽

Yidong Cai ◽

Jingjie Yao

Keyword(s):

Hydraulic Fracturing ◽

Coalbed Methane ◽

Continuous Production ◽

Fracture Morphology ◽

Geological Structure ◽

In Situ Stress ◽

Gas Production ◽

Type Curves ◽

Stable Type

Hydraulic fracturing has been widely used in low permeability coalbed methane reservoirs to enhance gas production. To better evaluate the hydraulic fracturing curve and its effect on gas productivity, geological and engineering data of 265 development coalbed methane wells and 14 appraisal coalbed methane wells in the Zhengzhuang block were investigated. Based on the regional geologic research and statistical analysis, the microseismic monitoring results, in-situ stress parameters, and gas productivity were synthetically evaluated. The results show that hydraulic fracturing curves can be divided into four types (descending type, stable type, wavy type, and ascending type) according to the fracturing pressure and fracture morphology, and the distributions of different type curves have direct relationship with geological structure. The vertical in-situ stress is greater than the closure stress in the Zhengzhuang block, but there is anomaly in the aggregation areas of the wavy and ascending fracturing curves, which is the main reason for the development of multi-directional propagated fractures. The fracture azimuth is consistent with the regional maximum principle in-situ stress direction (NE–NEE direction). Furthermore, the 265 fracturing curves indicate that the coalbed methane wells owned descending, and stable-type fracturing curves possibly have better fracturing effect considering the propagation pressure gradient (FP) and instantaneous shut-in pressure (PISI). Two fracturing-productivity patterns are summarized according to 61 continuous production wells with different fracturing type and their plane distribution, which indicates that the fracturing effect of different fracturing curve follows the pattern: descending type > stable type > wavy type > ascending type.

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