![]()
Summary Development of simultaneous downhole flow-rate/pressure measurementequipment has permitted better determination of reservoir properties. Application of such equipment to layered reservoirs allows determination ofindividual layer properties. This paper reviews state-of-the-art pressure andflow-rate devices, discusses the advantages and limitations of specificequipment, and ad-dresses the need to evaluate current tools and areas forfuture research.
Introduction Various dynamic downhole measurements (e.g., pressure, flow rate, temperature, and density) are routinely performed simultaneously bywell-testing and production logging devices. Production logging surveys understabilized flow (or shut-in) conditions are useful to diagnose and monitor wellperformance. Such surveys can be conducted by dynamic tool passes across theformation and/or by stationary measurements between producing zones. Stationaryreadings may also be used to measure the reservoir's transient response toflow-rate changes. Results are used to quantify well performance. Anotheruseful application of simultaneous performance. Another useful application ofsimultaneous flowrate/pressure measurements is the determination of the effectsof reperforating on reservoir performance. Simultaneous flow-rate and pressuremeasurement is a powerful technique for reservoir property determination inboth single- and multilayered reservoirs. Such measurements may be obtainedwith tool combinations ranging from "full-spectrum" production loggingstrings to much more abbreviated tool configurations. The purpose of this paperis to describe state-of-the-art equipment for the measurement of downhole flowrate and pressure. Advantages and limitations of current tools are discussed. This paper illustrates how some inherent measurement errors can affectcomputation of reservoir properties from pressure-transient test analysis. Future research areas are also addressed.
Pressure/Flow-Rate Equipment Combinations Pressure/Flow-Rate Equipment Combinations Sensitive electronic pressure devices, such as the quartz crystalgauge, have revolutionized pressure-transient testing. 3.4 The ability tocombine downhole pressure-transient and flow-rate measurements simultaneouslyallows improved analysis of conventional pressure-transient tests and oflayered reservoirs. pressure-transient tests and of layered reservoirs. Theproper combination of downhole pressure gauge and flowmeter depends on downholeflow parameters and the type of information required. For example, pressure/flow-rate tools for a conventional buildup test will differ from thoseon a string used to run a full-spectrum production log before buildup testing. The choice of spinner-type flowmeter will frequently he dictated by suchdownhole conditions as rate, water cut, wellbore deviation, and casing size. Whether a basket-type flowmeter is required depends on the same flow conditionsand on the type of logging data desired. The choice of a sensitive quartzpressure gauge over another device is likewise dictated by test designconsiderations. A quartz pressure gauge is a popular choice for mostpressure-transient testing applications because of its high degree ofpressure-transient testing applications because of its high degree of accuracyand sensitivity. Such gauges also are commonly used for absolute pressuremeasurement during production logging operations. One major wireline contractoruses a strain-gauge sensor to make combined pressure and fluid-densitymeasurements during production logging. This device can he used alone or withthe more production logging. This device can he used alone or with the moresensitive quartz gauge when more accuracy for pressure transient analysis isrequired. Flowmeters are currently limited to several varieties of spinnertools. The conventional "continuous" spinner tool and a"turbine" spinner analog perform well during production loggingoperations in high-rate wells. Therefore, they frequently are used mpressure-transient testing applications. The "fullbore"pressure-transient testing applications. The "fullbore" flowmeter (Fig.1), a variation of the conventional continuous flowmeter, is designed toprovide a more representative fluid-velocity measurement in multiphase flow, especially in deviated wells. The fullbore flowmeter uses various bladediameters to accommodate the full range of casing sizes. Rate measurement inlow-rate wells, especially in deviated offshore wells, is enhanced by use ofone of a variety of basket-type flowmeter. Such devices are designed to measureall flow with petals that seal against the casing. A more recent variation ofthe petals that seal against the casing. A more recent variation of the basketflowmeter, the Inflatable Diverter Flowmeter (Fig. 2), is designed to provide amore linear tool response.
Equipment Evaluation Flowmeters. Continuous Spinner Continuous spinners derive their name fromthe fact that multiple logging passes are usually made under stabilized flowconditions to produce a continuous log of spinner response vs. depth. Suchtools produce electrical pulses as the impeller is rotated; pulse rate isproportional to rotational speed, which in turn is related to fluid velocity. Spinner threshold velocity is the fluid velocity below which impellerrotational speed is zero. Positive threshold values result from the effects ofmechanical friction and fluid properties. Low threshold velocities are moreimportant in well-test analysis than in production logging applications becausetools are stationary during production logging applications because tools arestationary during pressure-transient testing and receive no benefit oftool-line speed, pressure-transient testing and receive no benefit of tool-linespeed, as occurs during dynamic passes. Retaining acceptable threshold valuesdepends heavily on proper tool maintenance. Fig. 3 illustrates turbine spinnerresponse from flow-loop measurements for monophasic oil in 6.5-in.-ID pipe. Wellbore deviation, even in single-phase flow, creates scatter in the data atrates below about 75 gal/min (2,550 B/D). A linear data regression for allrates and angles gives a threshold rate of about IS gal/min (510
Fig. 4 demonstrates the additive effect of biphasic flow and wellboredeviation on data scatter. Spinner response is angle-dependent at all ratesinvestigated. At rates below 90 gal/min (3,060 B/D), localized velocityreversals create reversals in spinner rotation, even though the tool is wellcentralized. Fig. 5 shows the turbine spinner response to a combined fit ofdata from monophasic oil and water flow in addition to biphasic flow over awider rate range. These data are for vertical flow. Deviated flow results arecomparable above 5,000 B[D. Fig. 5 also indicates the spinner"efficiency," i.e., the ratio of measured to theoretical response basedon impeller pitch. Flow-loop data illustrate that continuous spinner flowmetersdemonstrate predictable, linear response under high-rate conditions. Atmoderate rates, response depends more heavily on wellbore deviation and watercut. Low flow rates can produce uninterpretable measurements. Therefore, continuous spinners are most effective in testing multilayered reservoirs beingproduced at high rates. Use of such tools for buildup testing of single-layerreservoirs works best in high-rate gas wells, where higher wellbore storageallows better afterflow measurement.
SPEPE
P. 427
Site News