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In 1992, Chevron USA initiated a large waterflood program in the Belridge Diatomite at Lost Hills Field. Injection and production wells are hydraulically propped-fractured, and water is injected across a vertical interval of approximately 600 ft. The injected water is assumed to follow the hydraulic fractures and spread laterally outward. However, the extent of flooding, the saturation variations between individual layers, and the connection between waterflood patterns are poorly understood. During this same time period, crosswell electromagnetic technology was developed and tested in other fields in the San Joaquin Valley. This technology can provide an interwell resistivity distribution from wells separated by up to 1000 ft, and thus, may be suitable for mapping water saturation variation and reservoir structure. In this paper we describe the application of crosswell EM technology to several waterflood patterns at Lost Hills. The first cases involve surveys between closely spaced fiberglass-cased observation wells across and perpendicular to a hydraulic fracture. The interwell resistivity distribution identified the edge of the waterflooded region and mapped saturation variation between the layers that were affected by the flood. In another example, crosswell data that were collected parallel to hydraulic fracture planes show the connection of injection plumes and also significant saturation variation between layers. Introduction Producing oil and gas at the Lost Hills field is an ever-increasing challenge. Although over 2 billion barrels of oil is in place, oil production is difficult due to low matrix permeability and unusual formation properties in the diatomite. Operators are frequently plagued by issues of low production rates, ground subsidence and well instability. Chevron USA is testing a variety of technologies to improve both production and overall recovery. These include induced fracturing, and water, steam and CO2 floods. Most new technologies are tested in pilot studies. Considerable effort is expended to monitor the results of the pilot tests in order to track reservoir changes during production and injection, improve production and injection rates, better characterize existing resources, and determine the best alternatives for expanding the pilots and increasing oil recovery. As part of the waterflooding program, Chevron has established several pilot sites where a number of observation wells are drilled and new production, injection or monitoring technologies are tested. In two of these pilots, Chevron has installed two fiberglass-cased wells surrounding an injection well and has applied several logging technologies, as well as crosswell electromagnetics (EM) to evaluate the present status of the resource and to identify the progress of the ongoing waterflood. The crosswell EM technology is attractive because of its capability to map the interwell resistivity distribution. This, in turn, allows for convenient tracking of ongoing flooding operations as well as improved reservoir characterization. In this paper we will briefly describe the crosswell EM technology and illustrate its application to reservoir characterization using data collected at Lost Hills.

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.

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