SAMPLING ISSUES in KHUFFLIKE GAS CONDENSATE RESERVOIRS Sissel

SAMPLING ISSUES in KHUFF-LIKE GAS CONDENSATE RESERVOIRS Sissel Øksnevad Martinsen Curtis H. Whitson March 15, 2007 1

Summary of Ongoing Work n Study the variation of condensate-gas ratio (CGR) during short-term sampling tests. n Rate variation, CGR = f(qg) For a range of well kh products n Relative permeability effect n Layering effect n Rate sequence (Increasing/Decreasing) n Sampling Issues in Khuff-like Gas Condensate Reservoirs 2

Base Case* n n n n One geologic unit, uniform properties Reservoir Fluid: K 2 & K 3, Compositional simulation h = 1000 ft k = 5 md Nr = 200, Nz = 1 (Single well, r-z model) pi = pd qg range: 20 -200 MMcf/d Full-pressure BU between rates * Simulation model adapted from the paper: IPTC 10692 Khuff Gas Condensate Development (Whitson & Kuntadi). Sampling Issues in Khuff-like Gas Condensate Reservoirs 3

Sensitivities n n Relative Permeability Layering n A thin high permeable zone (HKLH) in the middle of a low permeable reservoir. n Multi-rate test sequence n Additional sensitivities: n n n Degree of undersaturation (pi > pd) Geologic layers with different reservoir fluids Degree of depletion Sampling Issues in Khuff-like Gas Condensate Reservoirs 4

Producing CGR is decreasing linearly with increasing gas rate. slope The slope is approximately inversely proportional to the kh product Sampling Issues in Khuff-like Gas Condensate Reservoirs 5

Understanding CGR – Rate Variation n Based on the Fevang-Whitson 3 -Region model, our hypothesis is that CGR-rate variation is mainly due to the change in p* with rate. n p* is defined as the dewpoint of the wellstream mixture and equals the pressure at the boundary of Regions 1 and 2. n p* is strongly coupled with the FBHP, pwf. Sampling Issues in Khuff-like Gas Condensate Reservoirs 6

Condensate Blockage Pressure Adapted from Fevang & Whitson paper: SPE 30714 Modeling Gas Condensate Well Deliverability Wellbore Reservoir Pressure Pd Dewpoint Pressure P* Pwf 1 2 r* 3 rd Distance Sampling Issues in Khuff-like Gas Condensate Reservoirs 7

p*, r* BHFP pwf Sampling Issues in Khuff-like Gas Condensate Reservoirs 8

CGR Stabilization qg = 100 MMcf/d n The CGR stabilizes more rapidly in the simulations with: n n Low kh product High production rate Sampling Issues in Khuff-like Gas Condensate Reservoirs 9

Relative Permeability Controlling Region 2 n n n The saturation exponents, ng & nog , are varied. Endpoint gas relative permeability is equal at initial conditions. The higher value of n, the higher drawdown and saturation buildup Producing CGR’s are lower for higher n at equal rates. Controlling Region 1 10

Flow-After-Flow Test n Multi-rate testing with increasing rates are recommended. n Time needed to stable CGR is shorter. If stable CGR is reached, the CGR vs. rate trend is equal to the full-pressure BU between rates. 11

Sampling Issues in Khuff-like Gas Condensate Reservoirs 12

Sampling Issues in Khuff-like Gas Condensate Reservoirs 13

Data from paper by Sage & Olds: Volumetric Behavior of Oil and Gas from Several San Joaquin Valley Fields Sampling Issues in Khuff-like Gas Condensate Reservoirs 14

qg= 180 MMcf qg= 120 MMcf qg= 60 MMcf Sampling Issues in Khuff-like Gas Condensate Reservoirs qg= 180 MMcf qg= 20 MMcf 15

*Figure from Fevang & Whitson paper: SPE 28829 Accurate Insitu Compositions in Petroleum Reservoirs Sampling Issues in Khuff-like Gas Condensate Reservoirs 16