Saving Time and Money with the SPIDR in the Rockies
By Chris Floyd |
Thu, 8 Nov 2007
As more and more wells are drilled in tight formations, new testing methods and data gathering techniques are required to optimize well performance. One major service company in the Rockies recently discovered that the SPIDR fit their stimulation testing needs perfectly. In many different environments, pressure build-up tests are perhaps the best method; however in wells with multiple, low perm pay zones, the time required to test each sand is prohibitive. In order to optimize multi-layer, low perm sand completions, a cost-effective method was needed to estimate pore pressure and permeability in each sand. The engineer called DRC to help him obtain the data he needed in order to design a frac for their customer. With frac schedules constantly changing, getting testing equipment to the field on time is crucial. DRC can ship anywhere over night (domestically) and can hotshot a SPIDR directly to your field location if needed. The SPIDR gave him the flexibility he needed for this job. He was so impressed with the results of the test; he plans on using the SPIDR on every injection fall-off test hereafter.
ìThe most significant limitation of postfracture well test analysis is the need for prior knowledge of reservoir permeability and pressure.î (SPE 49044) Multiple diagnostic fracture-injection tests can provide both, which allows reservoir quality to be ranked and the completion to be optimized. Also known as a Minifrac, FET (Fluid Efficiency Test), MFO (Mini Fall-Off Test), or DFIT (Diagnostic Fracture-Injection Test), the test is often performed prior to the stimulation treatment of a formation. It usually consists of pumping a small amount (500-2,000 gal) of water (often containing a clay control additive) into a sand at fracture rates (2 to 10 bbl/min). As in any well test, pressure and rate are measured throughout a fracture-injection test and recorded for subsequent analysis.
In specific areas where log-derived correlations had been used to determine reservoir pressure and permeability, it was found that, in depleted zones, this method was invalid. The DFIT or MFO was designed as a small injection test prior to fracture stimulation to correct these anomalies. Analysis of the Pseudo-radial flow period provides reservoir transmissibility and initial reservoir pressure.
ìA large amount of information is available from a simple pre-frac injection/falloff test to aid in fracture treatment design. The key requirements for the pre-frac injection test are fairly simple: High resolution pressure recording is mandatory. A normal service companyís gauge resolution of 5 to 10 psi is unacceptable. Ideally, a quartz surface or bottomhole gauge, with a resolution of 0.01psi should be used (SPE 39932).î ìBoth well testing and fracture modeling require the acquisition of specific data sets that are often considered too difficult or expensive to obtain based on the perceived value of the information.î (SPE 49044) Instead of an operator ìturn keyingî a fracture-injection test and its analysis, DRC offers a low cost, high resolution, alternative to data collection that could be used in conjunction with an independent pumping company or the operatorís own pumping equipment. DRCís SPIDR tool is installed on the wellhead in a matter of a few minutes by any field personnel in a fashion that does not intervene with the pumping unit and can continue to record wellhead pressures after the pumping unit has been removed. The analysis of the data could then be interpreted ìin-houseî by an outside consultant or by the company performing the stimulation. Significant monetary savings are seen, when utilizing the SPIDR for data acquisition and an independent pumping company to complete the test.
What appears to be a relatively small financial savings on each pre-frac injection test adds up fast when considering that hundreds of these tests are performed by operators in low permeability, ìtight gasî sands in the East Texas, South Texas, Mid-continent and Rocky Mountain regions every month. The injection test is gaining wider acceptance as analysis techniques continue to improve. These tests are especially useful in environments that require ìstagedî stimulation jobs where significant dollars are spent on stimulation related operations.
Reference:
SPE 49044 ìUnderstanding Fracture Performance by Integrating Well Testing and Fracture Modelingî
SPE 39932 ìApplications of Pre-Frac Injection/Falloff Tests in Fissured Reservoirs ñ Field Examplesî
SPE 90455 ìApplication of MFO to determine Reservoir Parameters and Optimize Fracture Designs in a Tight Gas Fieldî
Additional Readings:
SPE 56600 ìEstimating Pore Pressure and Permeability in Massive Stacked Lenticular Reservoirs Using Diagnostic Fracture-Injection Testsî
SPE 75717 ìPermeability, Pore Pressure, and Leakoff-Type Distributions in Rocky Mountain Basinsî
SPE 75701 ìDiagnostic Fracture Injection Test in Coals to Determine Pore Pressure and Permeabilityî
SPE 60291 ìAdapting High Permeability Leakoff Analysis to Low Permeability Sands for Estimating Reservoir Engineering Parametersî
