Notice to Oil and Gas Operators: Determining Top of Cement by Calculation for Compliance with Statewide Rule 13


Railroad Commission of Texas (RRC) rules require operators to report the top of cement (TOC) for cemented casing strings in accordance with Statewide Rule 13 (relating to Casing, Cementing, Drilling, Well Control, and Completion Requirements). The most common method of determining TOC involves a volumetric calculation. Different equations and assumptions, including a washout factor, may be used when performing this calculation.

As part of the Texas Oilfield Relief Initiative, the RRC has modified the equation used to calculate the TOC to be consistent with the industry practice for calculating excess borehole volume. The improved accuracy of the RRC calculations saves both the agency and the operators time previously involved in resolving discrepancies between the RRC-calculated and the operator-reported TOC.

The RRC has also reviewed the baseline washout factors used in RRC calculations. The RRC has long used a baseline washout factor of 20 percent across most of the state, and 30 percent in coastal counties due to higher probabilities of encountering unconsolidated sands in the coastal region. Unless presented with evidence supporting adjustments on a county-by-county basis, the RRC will continue to use these baseline washout factors.

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