A Method for Predicting Depletion Performance of a Reservoir Producing Volatile Crude Oil

Abstract

Published in Petroleum Transactions, AIME, Vol. 210, 1957, pages 27–33. Paper presented at Petroleum Branch Fall Meeting in Los Angeles, Oct. 14–17, 1956. Abstract Future depletion performance and ultimate oil recovery from reservoirs producing under volumetric control are often predicted with the aid of a material balance equation. when the reservoir fluid is very volatile, however, certain assumptions implicit in the use of the conventional methods are no longer valid. This is because laboratory differential vaporization test procedures do not adequately represent the reservoir depletion process and the performance of surface separation facilities. In such cases recovery of stock tank oil per unit of pressure decline can be predicted only from a detailed knowledge of the separator conditions and the over-all composition of the fluid entering the wellbore at each stage of depletion. Surface recovery is not simply related to the total quantity of liquid flowing into the well under reservoir conditions. In order to improve predictions for reservoirs which produce volatile oils, a stepwise method of calculation has been developed. This method uses relative permeability data and multi-component flash calculations to predict oil and gas production as a function of reservoir pressure. Calculations are presented for a reservoircontaining a volatile crude oil, and predicted tank oil recovery by primary depletion is more than twice that predicted by conventional methods which are known to be adequate for ordinary black crude oils. Calculated maximum produced gas-oil ratio is less than one-fourth of the conventional prediction. Wellstream compositions have also been used to determine variation in stock tank oil composition and liquid content of the separator gas. This information is of particular importance for crude stabilization calculations and for design of gasoline plant facilities to recovery LAG and natural gasoline.

PVT Measurements on Petroleum Reservoir Fluids and Their Uses

“…An effort (28) to bridge this gap was made by "fitting" a set of /f-values to volumetric data on a particular reservoir fluid, and it was assumed that the /f-values thus obtained have validity over the range of compositional variations encountered as this same fluid undergoes pressure depletion in a reservoir. Since work of this nature is believed to hold major promise for future work, it will be discussed in some detail.…”

“…Thereby, a set of quite accurate K-values are derived from limited experimental data (volumetric) which are far easier to measure than compositional data, and the resulting K's may be used for calculations involving a much larger series of mixtures than the few tested. Since these notions were first presented (28) they have been used increasingly (2,6). Standing (57) described a simpler procedure earlier, but regardless of historical origin, methods of this nature deserve more research attention.…”

Application of New Compositional Simulation Approach to Model Gravity Segregation In Volatile Oil Reservoirs

“…With deeper drilling, more reservoirs containing volatile crude oil and gas condensates have been found and the need for accurate and economic methods for studying the performance of such reservoirs has become important. In the early 1950's several material balance methods were used for reservoir performance predictions (e.g., Cook et al, 1951;Jacoby & Berry, 1957;Reudelhuber & Hinds, 1957). Cook et al (1951) presented a method of estimating future reservoir performance and oil recovery of highly volatile type oil reservoirs.…”

“…Fluid compositions were determined from laboratory data and the actual reservoir study was conducted. Jacoby & Berry (1957) developed a tanktype model which used vapour-liquid equilibrium (VLE) and composition dependent densities and viscosities. This method used relative permeability data and multi-component flash calculations to predict oil and gas production as a function of reservoir pressure.…”