Production Well Testing Utilizing a Mass Flow Meter

Abstract

SPE Members Abstract Metering equipment has been developed which can accurately measure the percent watercut in addition to the total flow rate of an emulsion stream. This makes possible the use of two-phase (liquid and vapor) vessels for accurate production well testing purposes. This alleviates the need to use more costly and less operationally efficient three-phase vessels. Introduction The future of domestic oil production will be closely related to the ability to optimize secondary and tertiary recovery processes. "Reservoir management" is a common term for this process of optimization and requires expertise in several disciplines. A key to successful management of a hydrocarbon resource is the acquisition, organization, and proper utilization of accurate data. The most important of these are production data obtained from well tests. Accurate production data, however, are sometimes absent, inconsistent, or uneconomical to obtain. This lack of data causes difficulty in properly evaluating the recovery efficiencies of different areas of a reservoir. A proper evaluation is both more difficult and more important in heterogeneous reservoirs. Traditional well testing techniques required the operator to obtain an instantaneous well-head sample of the wellstream to determine the watercut and subsequently the oil and water production rates. These rates are assumed to be valid and are assumed to be constant until the next well test is performed (typically one month). In high watercut wells, a small error in the watercut will result in a large percentage error in the oil production rate. Current well testing practices in mature waterfloods involve metering equipment and sampling devices which are difficult to calibrate and operate. This paper will describe a mass flow meter which can accurately and continuously measure the percent watercut as well as the total flow rate of an emulsion stream. This allows the use of two-phase vessels for very accurate production and eliminates the need to use more costly, less efficient, and less reliable three-phase vessels. MASS FLOW MEASUREMENT A brief description of the theory behind mass flow measurement and watercut determination will be given to enable the petroleum engineer to understand the concepts involved. Consider a flow element or section of pipe through which an emulsion of oil and water is flowing. By rotating the pipe in an angular direction about a fixed point as shown in Figure 1, a 'reaction' force to the angular force imposed by rotation will be generated. This 'reaction' force or more precisely, the Coriolis force, will be perpendicular to the direction of flow and the direction of rotation. In addition, the Coriolis force is related to the mass by the relationship (1) where F is the Coriolis force, m is the mass, V is velocity in the reference frame, and w is the angular velocity. DENSITY MEASUREMENT Meters have been available for several years which utilize the relationship above to measure mass flow. As is the case with metering equipment, improvements in design have occurred and the meter used by the authors took advantage of many of these new improvements. The unique ability of the meter which has not previous been possible with any mass flow meter is the ability to simultaneously measure not only the mass flow rate but also to relate the physical properties of the tube and the emulsion component properties (oil and water) to determine the watercut. P. 75^