C&P: “Propped Height Validation in Liquids Rich Organic Shales using Recovery Factor Analysis”
Well performance evaluation in liquids rich shales has received a lot of attention in the literature to date. While there are a variety of techniques available to estimate effective fracture lengths and areas, the simplest method so far involves a comparison of volumetric oil in place with estimated ultimate recovery from the wellbore. A hypothesis was proposed in a major West Texas project recently that suggested slickwater fracs were only developing 50 to 60 ft of effective propped height regardless of proppant volume pumped. This limited height was validated in several vertical pilot wells with radioactive proppant tracers. When the trajectory of the lateral was compared to the pilot well net pay distribution it was observed that the wells that remained in the limited “sweet spot” had significantly higher recovery factors than those that did not. In addition, when a recovery factor analysis was made of the expected propped interval 120 acre recovery factors the values were in the 8-10% range. When the analysis was done for the entire 300 ft +/- gross pay column above and below the propped interval the recovery factors dropped to 1-2%. In an effort to improve propped height a hybrid slickwater/borate XLG treatment was pumped into a vertical pilot well with tracers run in the proppant. It was observed that the propped height for the proppant pumped with the crosslinked portion of the job had a tracer height identical to the 50 to 60ft slickwater conveyed proppant height. The hypothesis there is that the disconnect between the 2-3 hour break times and the 24-48 hour closure times resulted in a proppant bank suspended in low viscosity fluids rather than the 500 cp +/- borate system. Subsequent vertical pilot work proposed to improve propped height includes the addition of fiber to help retard settling (Schlumberger’s HIWAY system), the use of N2 bubbles to support the proppant (Trican), and forced closure. With regard to forced closure a two pronged approach has been recommended. The first is to force close a vertical pilot well frac with proppant tracers to see if the technique can improve proppant distribution. Once that is validated it is proposed to force close a lateral completion using an annular coiled tubing frac to enable circulation of the proppant that flows back out of the wellbore. All three of these techniques are on the board at this time with results expected shortly.
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