The unconventional wells with the best net present value (NPV) are the ones you don’t have to drill and yet deliver additional reserve recovery. Sound like an oxymoron? It’s not. That’s essentially the value proposition for refracturing existing wells.
Refracturing is catching on as a way to boost the lackluster 4% to 8% recovery factors typical of unconventional shale wells. Operators can rejuvenate production, slow the decline curve and increase ultimate reserve recovery by restoring reservoir conductivity.
But it’s not as easy as it might seem. Not every well will benefit equally from refracturing. A successful refracturing program is dependent on a workflow process that starts with collecting completion and production information for a shale play and compiling it into a single dataset. Those data are used in the well screening workflow to identify which wells have the greatest potential and in the refrack economic model to determine what the refrack is worth.
Each well is examined based on productivity and the decline rate to determine future production potential. Certain combinations of productivity levels and decline parameters are used to help flag good refrack candidates. After screening and identifying the best well candidates, the workflow estimates post-refrack incremental production. The output from the workflow is integrated with a full financial model that helps determine each operator’s refrack economics.
As we learn more, a variety of other factors beyond productivity and the decline curve may prove to be positive indicators of refrack potential. These include:
- The pressure transient;
- Reservoir pressure;
- Perforation design;
- Fracture conductivity of the initial frack; and
- Proppant composition and concentrations used in the initial frack.
Following the well selection and economic modeling process, it is essential to complete a review of the initial completion design—including existing perforating clusters—and the condition of the wellbore. These factors have a significant impact on the viability of a refrack job and the potential return on investment. Does the initial completion make it technically feasible to reenter the well? Can existing stages and new stages be isolated for the necessary fracturing program? Is the quality of the wellbore sufficient for refracturing?
Data from the well screening and economic modeling workflow are used in conjunction with a model of the reservoir that captures the full scope of subsurface data to design the most effective refracturing program. The goal of the program is to:
- Enlarge the fracture geometry to enhance reservoir contact;
- Increase fracture conductivity compared to the initial frack;
- Use more suitable fracturing fluids;
- Reopen natural fractures;
- Get more lateral coverage in horizontal wells or initiate more transverse fractures; and
- Reorient fractures due to stress field alterations, leading to contact of “new rock.”
Results of a recent Baker Hughes analysis that employed its proprietary well screening and economic modeling workflow identified more than 1,000 Eagle Ford shale refrack candidates that potentially could be stimulated with a resulting positive NPV. That’s out of more than 8,000 horizontal wells in the play. In the Bakken, 1,900 candidates were identified out of 10,000 total wells.
A successful well selection and refracturing design program means operators can avoid time-consuming portfolio analysis for potential candidate wells and highlight opportunities to increase production and significantly boost reserves. The process also allows operators to effectively manage costs by limiting investments in wells that are not refracturing candidates and only investing in wells that can be rejuvenated—often at half the cost of new wells—not just once but multiple times. And it limits the requirements for costly new wells.
Based on the knowledge gained from refracturing existing wells, operators can optimize their future field development plans and construct and fracture wells with future refrack operations in mind. When we reach that level of effectiveness, recovery factors from shale plays will improve exponentially.
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