Multiphase Well Rate Measurements Applied to Reservoir Analysis

Abstract

The new technology of multiphase measurement has been widely adopted by the oil industry. The meters that utilize this technology are either permanently installed or periodic usage such as well testing during the flow back, well appraisal, trials, etc. The consistent, reliable and accurate flow measurement plays an important role in reservoir and production engineering. However, the industry trends show that many practitioners do not fully utilize the potential of continuous on-line measurements for reservoir and production engineering assessments. This paper will show how online multiphase measurement data can be applied to reservoir and production analyses and how additional useful results can be obtained. Field examples from the Gulf of Mexico (GOM) will be presented to support the process. To begin with, the paper reviews the role of pressure transient analysis (PTA) and flux rate for assessing the health of the reservoir. PTA gives useful information about the health of the well (skin) and the reservoir properties. It is an established analysis methodology that requires two important inputs, bottom-hole pressure and flow rate. If the flow rates are not accurate, then the results from PTA would be erroneous. Also, the calculation of down-hole flow velocity would be incorrect. These uncertainties could result in wells to be produced below or above optimal levels. Either case would lead to production loss or well damage and the need for remedial work-over. Unfortunately, the maximum safe-rate term is not easy to predict. With high producing wells, minor measurement error can create significant errors in related calculations for reservoir or well parameters. For instance, if the well flow velocity in the formation exceeds the critical velocity for fines movement, the formation fines would start moving. Once they are moving, the additional near-wellbore region damage would be created or the screen may get eroded. Production data analysis (PDA) such as Rate Normalized Pressure (RNP) analysis in conjunction with continuous flow rate measurements, provided by online multiphase meter, can be used to obtain additional reservoir parameters. In the applications discussed in this paper, the flow rates from the multiphase meters were extensively used for reservoir and well surveillance, flow assurance and the well production allocation. Introduction With deepwater (DW) high investment wells, many operators have chosen continuous (real time) reservoir surveillance. Otherwise, the well is operated "blindly" and the risk for well loss is high 1,2,3,4. By doing continuous surveillance, one has an early warning of the well condition and remedial action can be taken immediately. In the GOM, most of the DW reservoirs are high-permeability reservoirs. Reservoir and the near wellbore region parameters are changing with time. Sound reservoir management requires monitoring of these changes. To develop these reservoirs, substantial investment is required. Also, once on production these reservoirs require constant surveillance (e.g. compaction, skin/permeability change, flow assurance, slug tracking, etc). Lack of surveillance or misinterpretation of well behavior could have detrimental consequences. Numerous examples of the failed wells have been reported in the literature.1 The most common well failure is screen erosion, which is caused by excessive fluid velocity across the screen area. The screen erosion, aggravated with fines and the fluid velocity, is directly proportional to the flow rate.