Abstract

As the industry moves towards stacked development more information on temporal well interference is necessary to determine spacing, completion strategy, and ultimate recovery of the hydrocarbon in place. Initial hydraulic connectivity is expected in most stacked development, however the key question to answer is when individual wellbores separate themselves from each other and begin to produce unique reserves. Pressure testing can be done at the expense of delayed production from those wells that are shut in. In-depth microseismic data acquisition, coupled with a tracer program could illicit results, but the capital burden can be quite high. Is there a low cost option that could be used to assess well cross-talk and also answer some questions on kerogen-to-oil relationships?

Whole oil gas chromatography can be utilized to determine unique signatures from oils in different unconventional reservoirs. Compositional differences in petroleum products should exist as organic depositional environments, organic compounds differences, and organic diagenesis can all vary from target to target. Current targeting strategies place the wellbore within the mudrock that has the highest organic content and generative capacity. This places an assumption that produced petroleum should, generally, be a direct product from these generative intervals. However, high energy stimulations create hydraulic connections that can overlap these individual targets. This overlap can result in petroleum from one zone being produced from a wellbore that is targeting another. By approaching the problem geochemically, we can provide a low-cost option to determine temporal zonal communication.

Diamondback Energy completed a 3-well stacked pad that exploits the Lower Spraberry Shale, Wolfcamp A, and Wolfcamp B in Midland County. The company decided to assess if produced fluids from each zone could be successfully differentiated for future temporal analysis. Oil samples from the three laterals were collected and run through gas chromatography sequentially with other nearby Lower Spraberry and Wolfcamp B samples to provide a zone control sample. Allocation via comparison of inter-paraffin peaks was then conducted to ascertain zone characteristics. Additionally, carbon isotopic analysis of the whole oil and SARA components was done to provide further evidence of zone contribution and source-oil relationships. Finally, cutting samples from the build section and some of the horizontal were processed for kerogen carbon isotopes to complement the oil isotopic analysis.

Results and subsequent interpretation show that the Lower Spraberry, Wolfcamp A, and Wolfcamp B have unique characteristics when assessing inter-paraffin peak relationships. This confirms that we could utilize this technique to assess well “cross-talk” over the first 6-12 months of production. As the signatures begin to separate, we can assume that the wells are now draining unique reserves within each of their targeted intervals. Conversely, the isotopic analysis demonstrated that the source material from the Wolfcamp A and Wolfcamp B are nearly identical and exhibit a strong marine influence. The analysis of the Lower Spraberry isotopes suggests a more mixed organic depositional environment. These findings not only complement the oil GC analysis, but it also lends some evidence to interpret that the base of the Leonardian could be above the upper Wolfcamp, as some suggest it should be interpreted.