Proppant Selection: The Key to Successful Fracture Stimulation
Authors: Montgomery C.T. , Steanson R.E. 
Published: December 2007

Many proppants and mesh sizes are available for thedesign of a fracture stimulation treatment. When proppants-sand (Ottawa, Texas Mining, Unisil), proppants-sand (Ottawa, Texas Mining, Unisil), bauxite, intermediate-strength proppants (ISP), resin-coatedsand (RCS), precured resin-coated sand (PRCS) and Zprop-are considered, the principal questions seem to be, prop-are considered, the principal questions seem to be, "Which one do I select"" and "How should I use it?"Maximized, adequate, long-term productivity inlow-permeability reservoirs depends on fracture penetration and fracture conductivity. How to obtain deeply penetrating fractures that are contained and adjacent to the porous penetrating fractures that are contained and adjacent to the porous interval is one of the questions that challenge the industry. Another is how to obtain sufficient fractureconductivity to use the deep penetration effectively. This is a state-of-the-art paper that attempts to bring the current technology on proppants together. This paper discusses how to determine and to obtain sufficient fracture conductivity. Fracture conductivity is a function ofthe proppant properties (i.e.. strength, roundness, andfines content), closure stress, drawdown rate, formation properties (i.e., proppant embedment conditions), and properties (i.e., proppant embedment conditions), and resultant propped fracture width. The engineering, principles involved in the selection of-the proper type and principles involved in the selection of- the proper type and amount of proppant are supported with a case history.

Introduction

As we explore for reserves at depths exceeding- 10.00ft 13,048 in], the tendency is to find reservoirs that havelow permeability and contain natural gas. Because of thelow permeability of the formation, the natural rateof production and the drainage area are often too low toprovide a commercial well. provide a commercial well. Propped hydraulic fracture-stimulation treatments thatcreate deeply penetrating, highly conductive flowchannels can be used to increase both the rate of productionand the drainage area. Four factors control improvements in productivity (i.e., the productivity index) provided by hydraulic fracturing.Propped fracture area (sq ft). This is the area of thefracture adjacent to the porous interval that has beenpropped (length times height). All the fracture area propped (length times height). All the fracture area adjacent to the porous interval that is created have not bepropped, and only the fracture area adjacent to the propped, and only the fracture area adjacent to the productive porosity that is propped is considered an effective productive porosity that is propped is considered an effective area.Conductivity of the propped fracture (md-ft). Thisis a measurement of how well the propped fractureconducts the produced fluids. In addition to the effectof closure stress on the permeability of the proppant, factors such as embedment. proppant distribution, andresultant fracture width must be considered to determine theconductivity of the fracture at reservoir producingconditions.Reservoir permeability. This value is used todetermine the fracture conductivity required to use theproposed fracture penetration effectively. proposed fracture penetration effectively.Drainage radius. This value is used, as is reservoirpermeability, to determine the length of fracture needed. permeability, to determine the length of fracture needed. A long, fracture is needed if the well spacing is large andthe reservoir permeability is low.

Typical Well

To show how the principles that are described in this paperwork, we will use a typical gas well with the propertiesdescribed in Table 1.

Effect of Reservoir Permeability on Fracturing. Indeep, hot, low-permeability sandstone reservoirs, development of deeply penetrating fractures with adequate conductivity is important. Once reservoir permeability isknown, it is important to optimize the fracture length andconductivity by comparing treatment cost to expected production. The pressure drop along a propped fracture that production. The pressure drop along a propped fracture that has an insufficient flow capacity will limit the productionfrom a well. A fracture with excessive fracture capacityis not effective.

Fig. 1 can be used as a guide in the selection of the desired effective fracture length based on reservoir permeability. When the reservoir permeability is greater than permeability. When the reservoir permeability is greater than about 0.1 md, the desired fracture lengths are generally1,000 ft 1305 mi or less. In low-permeability reservoirs(kg, less than 0.1 md), production can be almost directly proportional to fracture length before boundary conditions are proportional to fracture length before boundary conditions are reached. With adequate fracture flow conductivity, thelonger the fracture, the higher the producing rate. For example, in very-low-permeability reservoirs (i.e., 0.001 to 0.0001 md), fracture half-lengths of 2.500 to 4,000 ft 1762 to 1220 nil can be used to increase production effectively. Fig. 1 shows that in the typical well example with a permeability of 0.03 md. a 1,300-ft [396-m]fracture half-length should be created and propped to achieve maximum production.

Effect of Fracture Conductivity and Fracture Length on Production. Fig. 2 was generated with a reservoirsimulators and shows the effect of fracture conductivity(Cf) and fracture half-length on production in dimensionless terms.

JPT

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