Metering Emulsions for Commingling With the Electronic Cut Computer
Authors: Droemer Dr. 
Published: December 2007

The phase-null electronic oil-cut computer and the positive displacement meter have been successfully used for measuring untreated oil field emulsions for royalty allocation of net oil produced. Two projects in the Quitman field and East Texas field involving the installation of 10 phase- null cut computers are described. As opposed to the periodic sampling technique of net oil determination, operation of the computer is continuous, and a read-out of net oil shipped to central treating facilities is available at any time. Experience to date shows the method to be practical, reliable and economically attractive. A high degree of accuracy is indicated. Application of this technique makes it technically plausible in the future for large blocks of various competitor-owned leased to be produced into central joint venture treating plants, thereby providing more efficient treating with greater economy for all operators.

Introduction

The ever-increasing rise in the cost of oil production has necessitated a never-ending search for more efficient producing methods. In making its cost-cutting contribution, oil field automation has evolved through various stages from automatic well controls (such as in the East Texas field) to common centralized batteries where production from many royalty accounts are commingled into common storage and shipped to the pipeline carrier by automatic custody transfer. As confidence was gained in the accuracy of the positive displacement meter, the common central battery concept received widespread acceptance. It follows that central treating of commingled lease production is the next step in streamlining; however, to assure accurate measurement of production before commingling, the Texas Railroad Commission by special field and state-wide rules requires pipeline-quality oil before metering. In some instances exceptions to this requirement have been granted, allowing metering of untreated emulsions into central treating facilities, provided a representative sample is taken at the time of measurement. The sample technique requires the lease operator to get a shake-out of each sample at the end of the accounting period to determine the quality of net oil to be allocated to each royalty account. This method presents the usual problems of obtaining a truly representative sample, and demands close supervision by the lease operator. The phase-null cut computer with positive displacement meter provides a means for continuously determining water cut and gives a digital number wheel read-out of net oil being measured, and thus is more compatible with long-range plans for the fully automated oil field. The results of pilot testing of this concept are given in this paper.

Phase-Null Cut Computer

The phase-null cut computer discussed in this report was developed by Shell Development Co., Emeryville, chiefly for use in well testing. A complete discussion on the theory of operation is not one of the objects of this report, because this subject has been covered thoroughly in previous technical reports and papers. A schematic layout of the cut computer along with a circuit diagram and a chassis photo are shown in Figs. 1, 2 and 3.Briefly, the phase-null uses the dielectric constant principle of determining water cut that has been used successfully in the familiar LACT BS and W monitor. By its electronic circuitry, the instrument measures changes in capacitance, or water cut, of fluids passing through the measuring cell. The circuit powers a servo-motor-driven capacitor (see Fig. 3) that constantly keeps the circuit in balance or "Phase null".

JPT

P. 1257ˆ