Increased Reservoir Contact in Cemented Multistage Completions In the Williston Basin, Using Engineered Diversion Workflow
Authors: Rondon Janz , Heaton Natalia , Lutken Gordon , Parker Jeff , Kothare Sunny , Porter Hank , Lowe Stephanie 
Published: April 2016

A new sequenced fracturing technique is presented that allows for further increases in reservoir contact in the developed multi-stage completion scheme utilized in the Williston Basin – cemented liner, plug and perforation. The performance of this composite diverter (or pill), with respect to stimulating more clusters and the resulting production, is evaluated using a detailed workflow in which real-time pressure observations are made, data is collected and analyzed using fracturing simulation tools, and production is compared with that of offset wells stimulated with conventional propped fracturing designs.

The success of the diversion will be presented as results from such analytic methods as observation of surface pressure responses to the pill’s placement into the formation, rate step-down tests for analysis of near-wellbore effects, and statistical evaluation of production data. The step-down tests provide comparisons of how many perforation clusters are stimulated before and after the pill, which will illustrate both the performance of plugging and diversion and the comparison to fracture counts in conventionally stimulated wells. Production comparisons between the test wells and offsets give an indication of increased reservoir contact resulting from diversion, and results from tracer collection illustrate which intervals (between diverter-treated and conventional) are contributing to production.

Over the 102 intervals in which the sequenced fracturing technique was implemented on the four cemented, plug-and-perf wells, significant diversion was observed in 97 of those, a 95% success rate. The success criteria for this condition were based on observation of increases in surface treating pressure at the constant-rate pill placement into the formation. Changes in instantaneous shut-in pressures (ISIP) before versus after the pill and overlays of treating pressure before and after the pill were also analyzed as metrics of diversion success, and it was found that 81% of test intervals met the success criteria for ΔISIP. Step-down tests indicated a reduction in perforations taking fluid from before the pill to after its placement, which supports the theory that this technique was effective in plugging fractures initially taking fluid.

The success of fracture plugging and diversion was reinforced by analysis of the near wellbore effects obtained from the step-down tests, which illustrated that the tortuosity reduction achieved by acid following the pill was significantly greater than the reduction observed during the placement of the first acid spear (following the ball) – indicating that new perforation clusters were being treated after the pill. Production data supported the theory that diversion and increased reservoir contact was achieved, due to the performance of test wells versus offset wells treated with similar, but conventional, hydraulic fracturing designs. The wells within the study on which diverter was pumped across the entire lateral produced, on average, in the 71st percentile among each of their groups of offset wells after 150 producing days. Three of these were P90, P81, and P80 wells, but the fourth cemented well, producing in the 31st percentile, due to increase in water cut after artificial lift pump installation.