This paper was prepared for presentation at the 1999 SPE/EPA Exploration and Production Environmental Conference held in Austin, Texas, 28 February-3 March 1999.
A new-generation borehole gravity meter (BHGM) and sonde have been developed and successfully operated under the rigors of a pressurized wireline logging operation in an Alaska North Slope solids injection well. The new BHGM addresses shortcomings of earlier technology, such as sonde diameter, maximum well deviation, depth correlation, reliability, and availability.Borehole gravity logging provides a large depth-of-investigation alternative to the very shallow formation bulk density measurement obtained with conventional nuclear density logging tools, and the measurement accuracy is close to that of a nuclear density log. Therefore, it is a candidate for density measurements in wells with large near-borehole effects such as invasion, mudcake, rugosity, and completion hardware that are detrimental to nuclear density logs. A BHGM is also well suited for reservoir injection applications, such as the present case study, where changes in the pore fluid, and therefore bulk density, are expected at large distances from the borehole (many tens of feet) and long times (months or years).We present the results of BHGM measurements made in a disposal well that has been receiving injected slurry of groundup drilling cuttings and water for 12 years. Descriptions of the well injection history and BHGM log are presented along with performance data from the gravity and depth measurements. The BHGM density log showed agreement above the injection zone with a pre-injection openhole nuclear density log, but showed a large increase in density at the injection region.Software for 3D gravity forward modelling, constrained by the known total mass of injected material and known porosity, provided a reasonable spatial model of the injected material in the formation consistent with the gravity measurements. This type of analysis, coupled with time-lapse BHGM measurements, can also be used in reservoir monitoring applications to visualize movement of waterflood fronts or gas expansion zones before they reach producing wells. IntroductionThe Prudhoe Bay field, Kuparuk River field, and other major oil fields are located on the northern coast of Alaska, approximately 300 miles above the Arctic Circle. Development wells were directionally drilled from gravel well pads. Drilling waste comprising mud and cuttings was originally stored in reserve pits, actually impoundment areas surrounded by areas of the pad and access roadways. The grind-and-inject (G&I) project was initiated to dispose of this stored waste to allow closure of the reserve pits. Today, new drilling waste and some production waste is also disposed of at the G&I plant.Waste is excavated during the winter and hauled to the G&I plant. It enters the plant by conveyor and is mixed with heated seawater inside a rotating ball mill. The ball mill reduces the mix to slurry which can be injected into one of three UIC Class I disposal wells. Injection is cycled among the three wells with a typical injection period in a single well of 1 to 2 weeks. In July 2010, approximately 124 million barr...
The main North Slope Class I industrial waste disposal facility has injected 12 million barrels into a permeable formation just beneath the permafrost at 2000 feet. Initial concerns about fluid confinement were addressed by extensive field testing. This testing, coupled with the absence of underground sources of drinking water, allowed injection pressures to be authorized above the fracture gradient - an unusual operating condition. Re-permitting the facility in 1999 required an evaluation of permafrost thermal response to the injection of warm fluids and determination of potential impacts on waste confinement. This was accomplished using temperature logging after a one week shut-in period and by thermal modeling. At issue was whether the temperature log profiles could be explained by conductive heat transfer or whether they indicated upward fluid movement out of the injection zone. The evaluation was accomplished by coupling a radial thermal model with a one-dimensional vertical conduction model. This combination could better predict the temperature profile adjacent to the injection interval because vertical heat transfer is dominant just above the storage reservoir. Very good agreement was obtained between field measurements and the model results, indicating there was no fluid moving upward through the confining zone. With this "history match" as a basis, the model was used to predict future temperature changes and thaw bulb growth throughout the permafrost interval. Introduction Five wells were drilled through the permafrost in 1973 for a field test to determine the thaw extent and casing loading that results from production of hot oil-reservoir fluids. The wells were located at the Prudhoe Bay Pad-3 facility and oriented on a 5-spot pattern with 33 feet between the corner wells (Figure 1). During this test, hot glycol was circulated in the five unperforated wells to thaw the permafrost. After 18 months, the individual thaw bulbs merged to form a single thaw bulb. This test and results are documented in Reference 4. Following the test, the wells were shut in until waste injection began in 1976 in the Northwest well. Injection began in the Northeast well in 1978 and in the two southern wells in 1985. Injection has alternated among the four corner wells during the past 23 years. The center well was never completed and the Northeast well was plugged and abandoned in 1988 due to mechanical problems. In 1989 three wells were permitted for Class I industrial waste disposal. The injected volume has now reached 12 million barrels (MMB). The wells are completed as shown in Figure 2. They are perforated 145–258 feet below the base of the permafrost in a heterogeneous interval of thinly-bedded sand stringers, siltstones, and mudstones. A very permeable 30 foot-thick sandstone comprises the upper part of the injection interval. The confining zone and arresting interval are composed of inter-bedded low permeability silts, shaley mudstones, and sand stringers. The aggregate thickness is 132 feet. Wastes are trucked to Pad-3 from various sources. These include drilling rigs, production facilities, well treatments, heavy equipment operations and maintenance, laboratories, and the de-watering of numerous pits. These volumes include a wide spectrum of waste types (1) (2) with a range of temperatures, viscosities, densities, and solids content.
Forest improvement harvests using individual-tree and group selection were conducted in four oak or oak-hickory stands in the Missouri Ozarks with conventional equipment (chainsaw and skidder). Volumes (and revenues) for different timber classes (sawlogs and smallwood from topwood and small trees) and hours of machine use were recorded to calculate production rates. Multiplying these by estimated hourly machine costs and adding loading and transportation costs plus stumpage yielded harvest plus delivery costs. Loggers kept machine costs low by operating old equipment with low capital costs and by owner servicing. Coharvesting of sawlogs and smallwood provided $240‐$340/person-day in net operating revenues to loggers. Smallwood harvest yielded positive net revenues because loggers paid little or nothing for this material. Nevertheless, loggers could continue to generate positive net operating revenues if they paid a modest fee of $4‐$5/ton for smallwood (as occurred in a subsequent salvage harvest). The cost of implementing best management practices (water bars and other erosion-control structures) with a skidder was affordable (≤2% of logger's net operating revenue). Overall, the results supported crop tree management as a financially rational alternative across a variety of sites and showed that smallwood harvest does not always require subsidy.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe main North Slope Class I industrial waste disposal facility has injected 12 million barrels into a permeable formation just beneath the permafrost at 2000 feet. Initial concerns about fluid confinement were addressed by extensive field testing. This testing, coupled with the absence of underground sources of drinking water, allowed injection pressures to be authorized above the fracture gradient -an unusual operating condition.Re-permitting the facility in 1999 required an evaluation of permafrost thermal response to the injection of warm fluids and determination of potential impacts on waste confinement. This was accomplished using temperature logging after a one week shut-in period and by thermal modeling. At issue was whether the temperature log profiles could be explained by conductive heat transfer or whether they indicated upward fluid movement out of the injection zone. The evaluation was accomplished by coupling a radial thermal model with a onedimensional vertical conduction model. This combination could better predict the temperature profile adjacent to the injection interval because vertical heat transfer is dominant just above the storage reservoir.Very good agreement was obtained between field measurements and the model results, indicating there was no fluid moving upward through the confining zone. With this "history match" as a basis, the model was used to predict future temperature changes and thaw bulb growth throughout the permafrost interval.
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