The Time-Dependent Permeability Damage Caused by Fracture Fluid
- N. Bostrom (Schlumberger) | M. Chertov (Schlumberger) | M. Pagels (Schlumberger) | D. Willberg (Schlumberger) | A. Chertova (Schlumberger) | M. Davis (Encana) | W. Zagorski (Range Resources)
- Document ID
- Society of Petroleum Engineers
- SPE International Symposium and Exhibition on Formation Damage Control, 26-28 February, Lafayette, Louisiana, USA
- Publication Date
- Document Type
- Conference Paper
- 2014. Society of Petroleum Engineers
- 1.8 Formation Damage, 1.6.9 Coring, Fishing, 5.1 Reservoir Characterisation, 5.6.1 Open hole/cased hole log analysis, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation
- permeability, water block, unconventional reservoirs, core analysis, pulse-decay
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Hydraulic fracturing causes a large amount of fluid to leak off into the reservoir, and the fluid is not recovered through flowback. The fluids enter the pore structure of the formation, and the presence of the invading phase blocks the in-situ phase. This event reduces permeability, particularly in unconventional reservoirs. Operators shut-in the well for an arbitrary time amount of time after fracturing to allow these phase blocks to dissipate. Conventional core flow tests and relative permeability evaluations using centrifuge drainage tests are unreliable—if not impossible—in these ultralow-permeability rocks.
In this paper, we present a method to measure the gas permeability on a core plug at reservoir conditions, both before and periodically after the plug was exposed to fracture fluid. The change in gas permeability over time allows optimization of the shut-in time. In addition, the combined rate of leak-off and imbibition is measured while the material is exposed to fluid. At the conclusion of the test, the axial water profile is determined by measuring unconfined compressive strength through by the mechanical scratch machine and water saturation with Karl Fisher titration. The measured dissipation time depends on the rock class as defined by Heterogeneous Rock Analysis which is based on the wireline log response.
The samples initially are saturated with gas and have the highest permeability. As the plug is exposed to water the permeability drops below the detection limit of 1nD. The water is removed from the face of the plug, water block is allowed to dissipate by capillary forces, and increases the permeability to 60% of the original value. Experimental results on core plugs from two major shale plays show that imbibition and fluid loss into ultralow-permeability rock can be substantial, but these processes are also highly variable. We have developed a measure of the phase block dissipation that is related to the material’s mineralogy, pore size distribution, and therefore, the log response. The information gives operators a quantitative measure to determine the length of shut-in periods and for the development of other methods to minimize the damage from water imbibition.
|File Size||1 MB||Number of Pages||17|