Reducing the Cost of Production Allocation by 95% Using a Geochemical Technique

Mark A. McCaffrey, David K. Baskin, Mark A. Beeunas, and Brooks A. Patterson
OilTracers LLC, Dallas, TX

A geochemical technique for quantitatively allocating the contribution of multiple zones to a commingled oil stream, or a commingled water stream, or a commingled gas stream (or any combination thereof) is preferable to production logging for several reasons. The geochemical technique costs <5% as much as production logging. In addition, the technique can be used in cases where production logging is not possible or is difficult (e.g., in wells with electrical submersible pumps, or in highly deviated wells, or in multi-lateral wells). The geochemical technique also does not interrupt production and eliminates the risk of sticking a logging tool.

Geochemical allocation of commingled production is readily achieved by identifying chemical differences between "end-member" samples (i.e., samples from each of the zones being commingled). Parameters reflecting these compositional differences are measured in the end-member samples and in the commingled samples. These data are used to mathematically express the composition of the commingled samples in terms of contributions from the respective end-member samples. Using a linear algebra approach, the concentrations (not ratios) of 30-80 components are used to simultaneously calculate the contribution of several discrete pay intervals (typically 2 to 6) to a commingled production stream. Iterative calculations are used to (1) “look for” and “delete” contamination in the samples, and (2) “test” the validity of the allocation results. These calculations are enabled by a commercially available software package, which is currently in use in numerous fields. Approaches for geochemically allocating production WITHOUT the use of end members will also be discussed.