Shared-Time Net Oil Measurement for Commingling Operations

Abstract

Abstract Electrical control over the discharge sequence for emulsion dumps from several separator allows one meter. probe and computer to measure separately, under pressure. the net oil from diverse ownership sources. Volumes from a lease-shared test separator may be included. Regulatory approval was granted and field use has commenced. Introduction Commingling untreated crude from diverse ownership sources for central treating and custody transfer commonly involves proportional allocation of central deliveries on the basis of lease net oil measurements. Equity maintenance obligation are met by using lease net oil measurement methods of equal quality, accuracy and reliability for all properties connected to the system. The difference between actual deliveries adjusted for central stock change and the sum of the lease net oil volumes for the month provides a continuing evaluation of commingling system performance. A lease net oil measurement unit (Fig. 1) costs about $2,500 and has a capacity exceeding 2,000 B/D. Many leases produce less than 200 B/D, and many multiwell leases need facilities for well testing that involve a net oil measurement separated from the remaining lease production being handled simultaneously. High initial investments can result from inefficient applications of equipment that occur when fieldwide modernization programs are attempted with separate measuring assemblies for production and well test functions needed on all properties. The shared-time net oil measurement method was developed to reduce both initial costs and future operating expenses required for lease measurements in commingling operations. It comprises electrical control of the sequence of discharge cycles from several emulsion source vessels that are connected to a single metering and measuring assembly. In effect, the multilease automatic custody transfer (ACT) control method is applied to the small-volume dumps under separator pressure from lease separators through a capacitance probe and meter assembly to achieve separate registration of measured net volumes by leases. The shared-time method has most of the merits and liabilities associated with its predecessor components. Multilease ACT Multilease ACT comprises the automatically controlled cyclic discharge of marketable oil, from two or more diverse-ownership atmospheric-source tanks, which is pumped through a single measurement assembly for custody transfer purposes. Float controls in the tanks activate attached electrical microswitches by float movement on the liquid surface in the tank (Fig. 2). Current flow occurring when the circuits are opened or closed by the switches can be termed "delivery start" and "delivery stop". These signals are transmitted to the control panel on the measurement assembly that includes the pump, meter and sampler. In a typical stepping switch scanner control action. the switch rotates in only one direction and its normal "home" position permits no current flow, When a delivery start signal is received, electrically driven rotation commences and continues until the "hot" contact is located. The action of associated relays in the circuit then holds the stepping switch stationary to start the pump, open the proper motor valve and engage the proper oil counters. When the discharge cycle from the affected tank is completed, as evidenced by receiving the delivery stop signal initiated by action of the lower float control on that tank, release of the relay then permits further switch rotation until home position is reached. En route, any other tanks that have reached delivery start condition are discharged similarly. JPT P. 1527ˆ