Summary In this paper, we present the fracture-compliance method, a technique for estimating the closure pressure from diagnostic fracture-injection tests (DFITs). The method is based on the observation that fractures retain a finite aperture after asperities come into contact (mechanical closure). An empirical, nonlinear joint-closure law is used to relate the after-closure fracture aperture and stiffness (the reciprocal of compliance) to effective normal stress. Fracture closure increases fracture stiffness, which, in low-permeability formations, causes an increase in the pressure derivative. On the basis of these insights, we propose the fracture-compliance method, which consists of picking closure at the first point of deviation from linearity on a plot of pressure or G×dP/dG vs. G-time (after the end of the very-early-time transient associated with wellbore and near-wellbore friction and fracture tip-extension). The contribution of this paper is to provide theoretical justification for why closure is best picked with the fracture-compliance method, and not with other widely used methods. We provide a series of numerical DFIT simulations to demonstrate the sensitivity of the pressure transient to input parameters. Governing equations are derived and used to demonstrate the effect of changing fracture aperture after closure. A field DFIT data set is analyzed with the new method. Finally, a field example is presented in which downhole tiltmeter measurements provide an independent estimate of the minimum principal stress.

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Re-examining interpretations of non-ideal behavior during diagnostic fracture injection tests, Journal of Petroleum Science and Engineering, http://dx. AbstractDiagnostic fracture injection tests (DFITs) are performed in low permeability formations to estimate the minimum principal stress, formation pressure, permeability, and other parameters. G-function derivative plots are used for diagnosing fracture closure and "non-ideal" reservoir processes. In this study, we use a discrete fracture network hydraulic fracturing simulator to investigate non-ideal DFIT mechanisms. The simulator fully couples fluid flow with the stresses induced by fracture deformation. DFITs are simulated for six different scenarios: a single hydraulic fracture, multiple fracture strands, opening of transverse fractures, near-wellbore complexity, far-field complexity, and height recession. The results indicate that pressure transient behavior commonly ascribed to "fracture height recession," "closure of transverse fractures," and "fracture tip extension" are likely to be misinterpreted by conventional techniques. In previous studies, we found that a curving upward G×dP/dG plot is caused by changing fracture stiffness after closure and that the closure pressure is best picked when G×dP/dG begins to deviate upward. In contrast, the commonly used "tangent" method can significantly underestimate the minimum principal stress. The results of this study confirm those prior results. The results suggest that in most cases, it should be possible to use pump-in/flowback tests to confirm estimates of the minimum principal stress. However, if a flow bottleneck occurs at the wellbore due to near-wellbore complexity, the pump-in/flowback test may be uninterpretable.

The Baldy Butte field is located in the East Washaltie subbasin of the Greater Green River Basin and is several miles east of the prolific Echo Springs/ Standard Draw Almond bar sand trend. Wells are completed in the upper 300 to 400 ft of the Almond formation (Upper Mesaverde), at a true-vertical depth of around 8000 ft. Production is wet-gas (10–14 bbl of condensate mmscf gas) and occurs from naturally fractured low-stand deltaic, marine and fluvial point-bar sand deposits. These sands are over-pressured (0.57 psi/ft gradient), possess an average permeability of 0.04 md, and exhibit variable continuity within the field. Most of the field development has occurred over the last 2 1/2 years, and has involved contrasting well-completion methods, each specific to the three companies that operate wells in the field. This paper documents an analysis of 29 recent, contiguous completions in the Baldy Butte field, comparing the effectiveness of the three contrasting completion stimulation methods. The evaluation was based primarily on use of the reciprocal productivity index (RPI) graphical production-analysis method. Using RPJ, daily production and wellhead pressure data for each well was used to dissect well performance, obtaining information on reservoir flow capacity, stimulation effectiveness, reservoir flow geometry, drained area/volume, and produced liquid management. Distinct differences in reservoir quality and effectiveness among the contrasting completion methods were observed. P. 307

This pqxr was selected for presentation by an SPS Program Canmittee fdlo.%ing rwiaw & information rnntdnad in an at@mct submitted by the author(s)Contenk of the paper, as pms.emkd, have not been radwed by the society of Petroleum Engineers and am subject to corractlon by the mdhor@). The material, as pr=ented, does not necessarily reflect any postion &the Sodsty C4 Petrobum Enginears, its offkers, or members. Papers presented at SPE medngs are subject to publc~on ravkw by Editorial Cunmittees d tie Scciety of Petroleum Engineam, Ebctmnii reprcdudon, distribution, or storage of any part of this paper for ccmnwcial purpc=saawithout tha written consent of the Scciaty of Petroleum Engineers is pmhibti, Permission to reproduce in print is restricted to an atstract d not more than 303 ihstrations may net be cqied. The abstract must contdn conspicuous ackmx,iedgment & tiere and by wlmm the pper was presented Write Librarian, S=, PO. Sox 833836, Rkhardaon, TX 750E3-=, U.SA., fax 01-972-952-9435 AbstractHydraulic fracturing of wells drilled in the Wasatch formation is a viable method of enhancing productivity. The Wasatch is a low porosity and low permeability, gas producing formation. It was deposited during the lower Tertkuy period in eastern Utah and is composed of a fluvial sandstone and shale. This formation is routinely fmctured as a completion method and genemlly requires crosslinked fracturing fluids that are not excessively viscous but are able to carry moderate to high amounts of proppant. As with most fracturing treatments, fracture clean-up and high conductivity are essential.