Fracture Dimensions in Frac & pack Stimulation
- Yong Fan (U. of Tulsa at National Inst. for Petroleum & Energy Research) | Michael J. Economides (Texas A&M University)
- Document ID
- Society of Petroleum Engineers
- SPE Journal
- Publication Date
- December 1996
- Document Type
- Journal Paper
- 403 - 412
- 1996. Society of Petroleum Engineers
- 1.8 Formation Damage, 5.2 Reservoir Fluid Dynamics, 2.4.6 Frac and Pack, 4.1.3 Dehydration, 3 Production and Well Operations, 2.4.5 Gravel pack design & evaluation, 2 Well Completion, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 2.5.2 Fracturing Materials (Fluids, Proppant), 2.4.3 Sand/Solids Control, 5.6.9 Production Forecasting, 4.1.2 Separation and Treating
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A model is introduced to predict dynamic fracture dimensions in frac&pack stimulation. Design aspects of the two-in-one step treatment techniques, required by soft and high-permeability reservoirs are discussed. A pressure-dependent leakoff model, based on the transient flow of a non-Newtonian fluid displacing a reservoir fluid has been developed and incorporated with fracture mechanics concepts to simulate the entire process of frac&pack treatments including fracture propagation, inflation, proppant packing and closure. Results obtained in this study indicate the considerable difference between traditional fracturing and frac&pack treatments. In the latter, fracture length is much less important than fracture conductivity. This work shows how to terminate the fracture growth at the appropriate time, and how to design frac&packs resulting in fracture widths several times larger than those for traditional fracturing.
Frac&pack, a combination of hydraulic fracturing and gravel packing, is emerging as an important, and with potentially wide applications, two-in-one step stimulation treatment to traverse near-well bore damage, reduce drawdown and control sand flow. This stimulation technique greatly extends the traditional permeability ranges of fracture candidates and has proven to be successful in well completions in the Gulf of Mexico, Prudhoe Bay, North Sea and other fields. The technique is particularly attractive when other forms of stimulation are rendered ineffective because of formation mechanical and chemical properties.
Historically, hydraulic fracturing has been used to stimulate the production or injection of low-permeability reservoirs where a moderate average propped width is sufficient to achieve high fracture conductivity. In such reservoirs, the well production or injection rate increases significantly as the fracture length increases, and hence massive hydraulic fracture treatments are executed routinely to obtain such large fracture lengths. Frac&packs, instead, are intended for moderate-to-high permeability reservoirs. The treatments require a large fracture conductivity which can be obtained from a large fracture width. Far smaller fracture lengths are created.
The desired conductivity can be obtained with two-in-one step treatments involving an intentional screenout at the tip of the fracture and then inflating and packing the fracture with a high-proppant-concentration slurry. The success of the treatment depends critically on the occurrence of the tip screenout at the designed fracture length and the ability to inject significant volumes of proppant after the screenout.
To design a screenout treatment, a somewhat inefficient fluid may be necessary such as a linear polymer solution with non-filtercake building characteristics. In the case of high reservoir permeability and in the absence of a filtercake, transient leakoff from the fracture face to the reservoir along with polymer invasion should be expected. However, most of the current treatment designs consider that the fluid leakoff remains constant with changes in applied pressure and conventional fracture simulators have been extended, with relatively little thought to frac&pack stimulation.
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