Abstract In an effort to examine well and reservoir connectivity for wells drilled through multiple low-permeability stacked lenticular reservoirs, we present case histories from the Piceance basin of Western Colorado. We review the completion and subsequent abandonment of an air-drilled high-angle slant hole through the Williams Fork sandstones in Grand Valley field as well as a high-angle slant hole drilled through and completed in two Williams Fork Mesaverde sandstones. We also review a case history describing single-entry-point fracture treatments in vertical wells designed to "frac into" sandstones near the entry point, and we describe a post-frac evaluation of propped fracture communication with sandstones adjacent to the single entry point. Lastly, we present a case history showing the results of a refracture-candidate evaluation and isolated-layer restimulation pilot program in the Piceance Basin where it is known that between 10% and 30% of the Meseverde layers targeted for fracturing are ineffectively stimulated or inadvertently bypassed during primary fracturing operations. The refracture-candidate pilot program provided the following. An evaluation of production logs as a refracture-candidate diagnostic. An evaluation of short-term pressure buildup tests as a refracture-candidate diagnostic. An evaluation of fracture-injection/falloff tests as a refracture-candidate diagnostic. Four discrete Mesaverde sandstones were tested as part of the refracture-candidate pilot program. Of the four layers selected for testing, numerous microseismic events were mapped during the initial fracture treatments in two, and no events were recorded in the other two. The refracture-candidate pilot program included recording a new production log and completing short-term pressure buildup and nitrogen fracture-injection/falloff tests in each isolated layer. The nitrogen fracture-injection/falloff tests confirmed the microseismic mapping during the original completion, that is, layers without microseismic events did not have a conductive hydraulic fracture based on the nitrogen-injection/falloff analysis. Consequently, bypassed or ineffectively stimulated layers can be identified with refracture-candidate diagnostics.

Summary The permeability, pore pressure, and leakoff type interpreted from more than 1,200 diagnostic fracture-injection/falloff tests were collected in a database and statistically evaluated for four Rocky Mountain basins. The statistical analysis includes the range of observed permeability and pore pressure and the fracture leakoff type distribution. The analysis reveals that pressure-dependent leakoff, fracture-tip extension during shut-in, and fracture-height recession during shut-in are the most common leakoff types. Overall, pressure-dependent leakoff, which can be indicative of highly productive fractured reservoirs, is the most common leakoff type in all Rocky Mountain basins. The analysis also shows orders-of-magnitude variation in gas permeability within all basins, with observed gas permeability ranging from less than 0.001 to greater than 0.10 md.

Permeability, Pore Pressure, and Leakoff-Type Distributions in Rocky Mountain Basins David P. Craig; David P. Craig Halliburton Search for other works by this author on: This Site Google Scholar Mike J. Eberhard; Mike J. Eberhard Halliburton Search for other works by this author on: This Site Google Scholar Chad E. Odegard; Chad E. Odegard Halliburton Search for other works by this author on: This Site Google Scholar Muthukumarappan Ramurthy; Muthukumarappan Ramurthy Halliburton Search for other works by this author on: This Site Google Scholar Rebekah Mullen Rebekah Mullen Colorado School of Mines Search for other works by this author on: This Site Google Scholar Paper presented at the SPE Gas Technology Symposium, Calgary, Alberta, Canada, April 2002. Paper Number: SPE-75717-MS https://doi.org/10.2118/75717-MS Published: April 30 2002 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Get Permissions Search Site Citation Craig, David P., Eberhard, Mike J., Odegard, Chad E., Ramurthy, Muthukumarappan, and Rebekah Mullen. "Permeability, Pore Pressure, and Leakoff-Type Distributions in Rocky Mountain Basins." Paper presented at the SPE Gas Technology Symposium, Calgary, Alberta, Canada, April 2002. doi: https://doi.org/10.2118/75717-MS Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex Search Dropdown Menu nav search search input Search input auto suggest search filter All ContentAll ProceedingsSociety of Petroleum Engineers (SPE)SPE Unconventional Resources Conference / Gas Technology Symposium Search Advanced Search AbstractThe permeability, pore pressure, and leakoff-type interpreted from more than 1,200 diagnostic fracture-injection/falloff tests were collected in a database and statistically evaluated for four Rocky Mountain basins. The statistical analysis includes the range of observed permeability and pore pressure and the fracture leakoff-type distribution.Specially designed "mini-frac" or diagnostic fracture-injection/falloff tests were routinely implemented throughout Rocky Mountain basins beginning in late 1998 for the sole purpose of estimating reservoir-engineering parameters. Using three recently developed analysis methodologies, more than 1,200 tests have been analyzed to determine permeability, pore pressure, and leakoff type.The analysis reveals that pressure-dependent leakoff, fracture-tip extension during shut-in, and fracture height-recession during shut-in are the most common leakoff types. Overall, pressure-dependent leakoff, which can be indicative of highly productive fractured reservoirs, is the most common leakoff type in all Rocky Mountain basins. The analysis also shows order-of-magnitude variation in gas permeability within all basins with observed gas permeability ranging from less than 0.001 md to greater than 0.10 md.IntroductionEstimating pore pressure and permeability in multilayered low-permeability gas reservoirs can be time consuming and, in a few cases, cost prohibitive. Because of the incremental costs and time required to implement a testing program, very few conventional well tests are completed in multilayered low-permeability gas reservoirs, even though optimizing completions requires knowledge of permeability and pore pressure.1As an alternative to conventional well testing, Craig and Brown2 suggested that conventional breakdown treatments in multilayered formations could be used to estimate permeability and pore pressure. Their procedure required isolating each reservoir, performing a small-volume injection, and recording the pressure decline during a shut-in period.2 In low-permeability reservoirs, a small-volume, low-rate injection will propagate a hydraulic fracture, and during the shut-in period, the pressure decline can be analyzed to estimate pore pressure and permeability. Craig and Brown2 advocated conventional leakoff analysis for estimating gas permeability, but before-closure pressure-transient analysis3 and after-closure analysis4 provide more realistic estimates of gas permeability.Craig, Eberhard, and Barree5 recently described the use of G-function derivative analysis and modified Mayerhofer permeability analysis for estimating pore pressure and permeability from the before-closure pressure decline following a fracture-injection test. The authors concluded that, when used in conjunction, the two techniques provide "reasonable" pore pressure and permeability estimates that are consistent with well performance based on reservoir simulation.5 Reservoir simulation in other multilayered low-permeability gas reservoirs also confirms that reasonable estimates of pore pressure and permeability are often obtained from before-closure analysis.6,7 Keywords: leakoff-type distribution, upstream oil & gas, reservoir, flow in porous media, fracture-injection falloff test, fracture closure, closure, gas permeability rad, gas permeability gdk, hydraulic fracturing Subjects: Hydraulic Fracturing, Reservoir Fluid Dynamics, Formation Evaluation & Management, Flow in porous media, Drillstem/well testing This content is only available via PDF. 2002. Society of Petroleum Engineers You can access this article if you purchase or spend a download.

Abstract The objective of diagnostic fracture injection tests is to optimize multi-sand completions by estimating pore pressure and permeability in each lenticular sand. Since December 1998, over 200 diagnostic fracture injection tests have been pumped into isolated Piceance Basin Mesaverde sands in an effort to optimize well completions. The diagnostic injection tests were implemented to qualitatively identify the presence of fractures/fissures, to provide estimates of pore pressure and permeability, and to optimize the perforation scheme for effective limited entry fracture treatment diversion. This paper describes the diagnostic fracture injection test methodology, summarizes the results, and provides illustrative examples of typical Mesaverde sandstone pressure falloff response. The results from 201 diagnostic fracture injection tests show extreme differences in reservoir quality between sands with very similar openhole log signatures. While approximately half of the injection tests indicate open fractures/fissures through pressure-dependent leakoff, it is quite common to observe relatively high-permeability (kg > 0.050-md) without indications of open fractures/fissures. Permeability estimates between pay sands separated by less than 50-ft have been observed from kg < 0.001-md to kg > 0.100-md. Several examples of sands damaged by drilling mud invasion (fracturing) have also been verified with the diagnostic injection test analysis, which can differentiate between reservoir fluid permeability and fracture face damage. Since the differences in reservoir quality are identified with a pre-frac diagnostic injection test, the final perforation scheme can also be adjusted to ensure a limited entry fracture treatment will divert to the "best" reservoir rock. Although the results presented are specific to the Piceance Basin, the methodology and analytical techniques are valid in all basins.