FridayNov4_Notes - .M u/A /H Va'GCOgE’Hf o? 0“...

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Unformatted text preview: .M u/A /H Va'GCOgE’Hf o? 0“ Imf_€.(,fflf/{afl Twsiow FLA-[a gamleg Coefficient of Viscosity of Oil (p0) At a constant temperature, the oil viscosity will vary with pressure as shown in the following diagram. Why does the oil visosity decrease as the pressure increases below the bubble point pressure? MW. a m =3“: ,l :5 t: \I/ Why does the oil visosity increase as the pressure increases above the bubble point pressure? 8-33 Coefficient of Oil Viscosity (’40) (continued) Applications of the coefficient of oil o I . vrscoslty. m The equation for predicting the oil flow rate from a cylindrical reservoir into a cylindrical wellbore (in oilfield units) is l/qo koh(Pe — Pw) (25) I ' -. l' 141 .2/ ,BO[I i) + s ] , l- r _/ W where q0 = oil flowrate, STB/ Day k0 = effective permeability of reservoir rock to oil, millidarcy h = reservoir pay thickness, ft pe = reservoir pressure at external radius (absolute), psia pw = wellbore pressure (absolute), psia S = skin factor, dimensionless re = external reservoir drainage radius, ft rw = wellbore radius, ft Bo = oil formation volume factor, RB/STB p0 = oil viscosity, cp Note the role of coefficient of oil viscosity. What is the oil tlowrate in RB/ Day? lnterfacial Tension (a) This is the contractile force that develops at the interface of two immiscible fluids due to unequal molecular attractions at the interface. This force causes the interface to act as a membrane. The interfacial tension between a pure liquid and its vapor (or air) is usually called the surface tension. lnterfacial tension (surface tension) is usually expressed in units of dynes/cm. w EAK ATTRACT1VE FORCE IN THE GAS I“ of? \r’ STRONG ATrRACTNE FoRCE N THE LIQMTD -35 CHAPTER 10 The five major tests and measurements normally performed in the laboratory on black oil samples are: - Composition measurement """ 0 Flash vaporization test 0 Differential vaporization test - Separator tests - Oil viscosity measurement 10- Sources of PVT Data 1. Laboratory Measurements 2. Correlations (Charts) 3. Calculations using the principles of thermodynamics, especially Equations of State 10- ix) 8.com 0+ EZV .62, 830: 629: < mcozfl at on— mhmm {A}. .6233. coast umfiiEzm .5 nmmmEmo cozohoamm moofiéBH «comb .waomn. 2:8. xuowwv Eomk . Emma. m .2938 F 55.33 .__ozmmmm onmn. age: @530 comfisuEm 10— Nomenclature for Flowing Well = pressure at external drainage boundary = average reservoir pressure = pressure of separator 1 pressure of separator 2 tubinghead pressure flowing bottomhole pressure reservoir thickness reservoir permeability permeability of damaged or stimulated region well's drainage radius radius of damaged or stimulated region = wellbore radius = temperature of separator l = temperature of separator 2 = reservoir temperature = total moles of well fluid entering separator l = moles of gas from separator ‘l = moles of liquid from separator l 10- Nomenclature for Flowing Well (continued) total moles of well fluid entering separator 2 (Note that n2 = n”) moles of gas from separator 2 moles of liquid from separator 2 composition of the liquid from separator l composition of the liquid from separator 2 composition of gas from separator l composition of gas from separator 2 total composition of well fluid entering separator 1 total composition of fluid entering separator 2 (Note that Zi2 = X“) 10- Sources of PVT Data (continued) Laboratory Measurements: Best source of PVT data. Costs money. Typically $20,000 to $30,000 per fluid study. An example fluid study for a black oil reservoir is presented in Chapter 10 of McCain. Special fluid studies for volatile oil and retrograde condensate gas reservoirs are also available. However, they are not discussed in McCain. Sample reports are enclosed with these notes. 10» Sources of PVT Data (continued) Correlations: Not as accurate as laboratory measurements. Give approximate estimates. Should only be used in the absence of laboratory measurements. Various correlations for estimating PVT properties are presented in Chapter 11 of McCain. 10- Sources of PVT Data (continued) Calculations using Thermodynamics (Eguations of State}: Requires the use of computers. Calculated results may need to be fine-tuned with some laboratory measurements. Aspects of this approach to PVT analysis are presented in Chapters 4, 12, 14 and 15 of McCain. 10- 8 Fluid Sampling Methods There are two methods for obtaining fluid samples for laboratory PVT measurements: 1. Subsurface Sampling 2. Surface Sampling Regardless of the method of sampling, it is important that fluid samples be collected early in the life of the reservoir to ensure representative samples. For an undersatured oil reservoir, samples should be obtained while the reservoir pressure is still above the bubble point pressure of the oil. If the reservoir pressure falls below the bubble point pressure of the oil, then free gas will form in the reservoir. It then becomes difficult to obtain representative fluid samples for PVT measurements. 10- 9 Fluid Sampling Methods (continued) Subsurface Sampling: An oil sample is captured downhole at the bottom of the well using a fluid sampler run on wireline. The SWPW kit/1056A at Bur; A6 Hm Simulate i6 WMbe “19) Method gives good and representative samples 7‘ (stemme- when the bottomhole pressure is above the bubble point pressure of the oil. Why? This method is not appropriate if the bottomhole pressure is below the bubble point pressure of the oil. Why? This method is not appropriate if the well produces a large amount of water. Why? The major limitation of the method is that only a small volume of sample can be obtained. Typically, 200 to 500 cc because of the limited volume of the sampler. 10- 10 Fluid Sampling Methods (continued) Surface Sampling: Oil and gas samples are collected at the first stage separator and recombined in the laboratory to obtain a representative sample for laboratory measurements. Before collecting the samples, the well is normally conditioned by producing it for a day or two for the well performance to stabilize. The producing gas oil ratio is measured and used to recombine the oil and gas samples in the right proportion in the laboratory to obtain a representative tluid sample for laboratory PVT measurements. 10— 1] Fluid Sampling Methods (continued) Surface Sampling Continued: The method can be used even if the bottomhole pressure is below the bubble point pressure of the oil provided that the reservoir pressure is above the bubble point pressure of the oil. This is the only valid method for obtaining samples from gas reservoirs. A major advantage of surface sampling is that large volumes of samples can be collected. 10- 12 ...
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This note was uploaded on 11/25/2011 for the course MATH 325K taught by Professor Shirley during the Spring '11 term at University of Texas at Austin.

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FridayNov4_Notes - .M u/A /H Va'GCOgE’Hf o? 0“...

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