ChevronTexaco has developed leading edge data acquisition and interpretation strategies to monitor steamfloods in Sumatra, Indonesia and San Joaquin Valley, California. This paper reviews ChevronTexaco's current steamflood surveillance techniques, and how learnings from San Joaquin Valley are adapted to operations in Sumatra. Introduction The Kern River field is one of the oldest and largest oilfields in California and has been produced for over 100 years. Oil gravity ranges from 10 to 15 API. Four major zones with multiple sands are present, each at varying stages of drainage. The Duri field is the world's largest steamflood. It was discovered in 1941, first production was brought on line in 1956, and steamflood operations were initiated in 1983. Oil gravity ranges from 17 to 23 API, and oil is highly viscous when cool (> 100 cP @100 degF). Two primary and several secondary producing zones with multiple sands are present. Time-lapse saturation and temperature profiles are developed from steam identification (pulsed neutron capture, cased hole neutron), Carbon/Oxygen, and temperature logs. Calibration of matrix Sigma in zones of 100% liquid saturation enables accurate steam/liquid saturation calculations using pulsed neutron capture logs. With the addition of a Carbon/Oxygen log measurement, a three-phase (steam/oil/water) saturation algorithm recently1 is applied to estimate remaining oil volume in the presence of steam chests. Cased hole log saturation calculations are validated against open hole saturations and core measurements. The time-lapse profiles are then applied to find bypassed oil, estimate remaining reserves, identify depleted zones, and influence steaming strategy. As steam is the single largest operating expenditure in both Kern River and Duri fields, it is imperative to use it wisely. Duri Field, Sumatra The Duri field is the world's largest steamflood. It was discovered in 1941, first production was brought on line in 1956, and steamflood operations were initiated in 1983. Figure 1 shows the Duri Field location and Duri Area map. Current production in Duri is 215,000 BOPD. Duri oil gravity ranges from 17 to 23 API, and oil is highly viscous when cool (> 100 cP @100 degF). Figure 2 shows a type log for the two primary producing intervals Pertama and Kedua. Secondary producing intervals are Rindu, Baji Jaga, and Dalam. In Duri, there is on average 1 temperature observation (TO) well every 45 acres. Duri has 1500 injectors, with three times the steam injection volume of Kern River. The current surveillance program in Duri consists of:Temperature profile in TO wells - 100% of TO wells surveyed once per yearTemperature profile in producing wells (Fiber Optic) - 5% of producers surveyed once per yearSteam IDentification (SID) / cased hole neutron - not used in DuriPulsed Neutron Capture (PNC) Sigma - 75% of TO wells surveyed once per yearKrypton/spinner profile in injectors - 50% of injectors surveyed once per yearCarbon/Oxygen (C/O) - 5% of TO wells surveyed once per year Kern River Field, California The Kern River field is one of the oldest and largest oilfields in California and has been produced for over 100 years. The location of the Kern River Field is shown in Figure 3.
Over the field life, surveillance in Tengiz oil field has provided historical and baseline data for simulation history matching, static and dynamic reservoir characterization and modeling, and the foundation for efficient well management. Hence, it continues to be an important part of everyday field operations. At the surveillance planning stage, the comprehensive opportunity list of well candidates is developed based on input provided by members of multiple teams: geologists and petrophysists, production and reservoir engineers, drilling and field operations specialists. SCADA system, permanent downhole gauges (PDHGs) and multiphase flow meters (MPFMs) are widely implemented for production data acquisition and analysis. However, the majority of surveillance activities still need well intervention into the high pressure, high H 2 S concentration wellbores, often during harsh weather conditions. Each job execution plan is therefore focused on the safest procedure to obtain the necessary data. Each planned survey in the surveillance plan is ranked according to the value of information to be obtained, in order to help schedule the timing of surveillance based on plant production needs.The ultimate goal is to safely execute planned surveillance to support production optimization and field development work. This paper will highlight TCO success in addressing the different reservoir and well production uncertainties through a properly designed surveillance plan with both short and long-term objectives.
A PNS logging program was designed to evaluate the economic potential of vertical steamflood expansion and to identify bypassed oil, based on a comparison of oil saturations from a Pulsed Neutron Spectroscopy (PNS) log to conventional core in a Kern River field well. In the comparison, PNS log oil saturations agreed with those from conventional core within 5.4 saturation units 68% of the time (log accuracy: 1 = 5.4). From multiple passes of the PNS log, it was found, for one effective pass at 60 feet/hour that the measurement repeats within 5.7 saturation units 68% of the time (log precision: 1 =5.7). After the comparison of log to core, a multiwell logging program was designed to determine oil saturations for several reservoir zones above and below existing steam flood zones. The results were used to optimize patterns for future steamflooding. In addition, oil saturations were obtained for zones within the existing steam flood to determine the economic value and risk for producing bypassed oil. For a proposed vertical expansion project, Expected Value Decision Analysis showed a benefit/cost ratio of 39/1 of running three PNS logs in the project area. The fraction of the total uncertainty associated with simulated production was reduced from 72% before to 39% after running the PNS logs. In addition, the PNS logs identified several million barrels oil in place that had not responded to conductive heating. Introduction Determination of oil saturation through time in heavy oil steam flood programs is necessary for effective heat management and optimum field development. ft is difficult to obtain accurate water and oil saturations from logs to monitor depletion in the Kern River field (see Figure 1 for location map) due to fresh formation waters, low production rates, extreme temperature variations, complex wellbore mechanicals, and varying steam saturations. Other thin conventional coring, the Pulsed Neutron Spectroscopy (PNS) log, or Carbon/Oxygen log, has been the only viable method to measure saturations. For existing projects, accurate oil saturation determination is necessary to assess whether or not efficient steam processing of zones is occurring (Figure 2). P. 347
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe paper discusses an assessment, using Monte Carlo modeling techniques, of the advantages we could derive and challenges we would face in utilizing multiple sensors with a pulsed neutron (PN) source for cased-hole logging to obtain petrophysical parameters. Current PN devices are primarily based on two detectors, with source-detector spacing often similar among the various vendors. We consider four sensors to investigate three measurement types, 1) a pseudo-density through casing concept that shows the potential to distinguish between gas and tight zones, 2) computing oil saturation from Carbon/Oxygen logs with oil present in the borehole, and 3) estimation of Sigma and hence water and steam saturation from PNC logs. We illustrate the advantages of using modeling to study measurement concepts independent of specific tools. We identify areas of further research in basic measurement concepts using pulsed sources and in related radiation transport theory.
Pulsed neutron measurements are commonly used to locate gas behind casing and quantify steam saturation, but do not always yield desired results. Several parameters are utilized to identify gas and one parameter, the thermal neutron capture cross section, Sigma, is used to compute steam saturation. In the paper we report a mixed experience in identifying gas with these techniques, across fields, tools and vendors. Some parameters have worked well in some cases but have performed poorly in others. The uncertainty in steam saturation, computed using Sigma, is greater than those previously reported elsewhere. Modeling offers insight into the mixed results. It appears that in some cases the PNC-derived Sigma may yield erroneous steam saturation for a variety of reasons, including uncertainties in the input parameters and possibly an inherent nonlinear transport effect that increases as steam saturation increases. An alternative approach based on PNC pseudo-porosity is explored. Calibration of cased-hole tools in gas reservoirs, generic and local, open-hole baseline data and core analysis of complex rocks are essential. Currently, these are either nonexistent or infrequent. Introduction Pulsed neutron capture (PNC) technique, initially used to compute water saturation in high- salinity reservoirs (for example, Dewan, et al., 1973) and in log-inject-log experiments to determine residual oil saturation, was extended to locate gas (Blackburn and Brimage, 1978). It is increasingly being utilized to locate gas in complex conditions and quantify steam saturation in steam floods. In addition, inelastic data, normally used to compute oil saturation, are being used to complement PNC techniques to detect gas. Recent applications in complex conditions include:identification of gas caps to optimize perforation decisions and reduce production of associated gas in West Africa (Badruzzaman, et al., 1997),monitoring steam-chest growth and estimation of steam saturation in steam floods in California and Indonesia (Badruzzaman, et al., 1998; Harness et al., 1998; Zalan, et al., 2003.),locating shallow gas hazards in Gulf of Thailand (Pathanakitchakarnjaroen, et al., 2005) andlocation of pay and identification of swept gas zones in Gulf of Mexico. The technique is being considered to monitor CO2 sequestration in Australia. In addition to PNC techniques, inelastic counts have been utilized as an independent validation of gas behind pipe. Success with pulsed neutron (PN) techniques, involving either the capture or inelastic interactions, has been mixed. Location of gas cap to reduce production of associated gas has generally been successful in Nigeria. Monitoring steam growth with PNC techniques has been successful in steam floods in California and Indonesia. Quantification of steam saturation has been very accurate in California while less so in Indonesia. Locating shallow gas hazards in the Gulf of Thailand has been ambiguous. Pay identification in Gulf of Mexico has been usually clear, but not always.
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