lhe slit-face of Ike Wilming/(m oil field hur now suh.rided U$ much us 29 // at the center aj an elongated depression roughly coinciding wirh the field productive area. Tcr defer. Inine rhe compacting intervals, a mefhod wux developed to detect chunges in length of individual casing joints. Both re rervoir e vritnates and ca.iing joint meu.ruremenls indicated (t pf)re vidunt e If).m of at lea }-f 3 poro.rit y percent. Caring j(,in/ ItIt,(I$Itrt>IttcIIIs UIWJwere used 10 detect ctt~ing el(mga !ii]tz in zones rrf waler injection. The vertical expansion o/ the reservoir i.r rdso seen on the surjace a.s uplijl that now umonn t.! I(Jas much as 8 or 9 in. in /he area r of hea vic.kr injet/ion. Rate .pre.~wrc dutrt jro)lt injcction well.r in Wil. ))~ingtcrn plot as a trmt.~itional curve (m coordinate paper rftfher than showing a sharp cilange of slope as isnormally \c,ert when {Iverhard( n pres.rure iv exceeded. Engineer.ỹ c[wking in the field and fatniliar~vilh (he utrcon wlidated nature of the jortnarions could UOI reconcile the ratepre.wure performance with /ornla\ion fracturing. By interrelating the zonrd expan~ion and surface uplift with Ihc ra!e-pre.i {ure crdrvex atld the radial jfow equation. it war concluded lhat tile forntalitmr experietlce a change in pore wlunt e and pernteabilil y a.~pressures are increased.
Introduction Environment, Ecology, Pollution - these were called the "bywords of today" by William H. Curry, AAPG president, early in 1971. Others have termed the 1970's as the decade, that will be remembered for the surge of public consciousness for our environment. It is unlikely that any other industry has been affected more by this tide of public thought than the oil industry. Other industries are commonly tied to one aspect or problem area such as noise or air pollution, but the many facets of the oil business make it vulnerable to attack from all sides. It has been said that there is no force so strong as an idea whose time has come. It is rather obvious that the time for environmental awareness is here now. Almost any industrial complex has some noise, air, water, or visual pollution problem. However, the oil business is beset by one additional problem: oil is where you find it, and a producing operation cannot be moved to an area zoned for heavy industry. Therefore, the industry must go a step further in public relations and environmental controls. The problems of producing oil in an urban environment appear to have been extended by some as far as the North Slope. The City of Long Beach does not have a North Slope operation, but it is hoped that our experience in a visible and very sensitive location will be helpful to the industry as a guide to future operations.
Summary A method has been developed in Wilmington field, CA, for measuring oil zone compaction and expansion by the deformation in well casing. Possible formation compaction is also directly investigated by locating radioactive bullets previously placed in the formation. Early logging techniques were described fully in 1969. The addition of a downhole odometer and different recording techniques have improved measurement accuracy. Random joint lengths have been repeatedly measured and remeasured under field conditions with a standard deviation of 0.0159 ft [4.8 mm]. An alternative system, developed by Ruedrich et al., utilized multiple collar locators and specially milled casing joints. Both systems can be applied to field situations where random joint lengths are found; however, the odometer system should be more accurate under these conditions. Introduction The basic problems of surface subsidence and related formation compaction in Wilmington field are well known. Field investigations have shown that when the formation rocks are unconsolidated, formation compaction and expansion are approximately reflected by casing length changes. Formation compaction is not reflected exactly by casing deformation because of slippage between the formation and pipe. However, in Wilmington field correlation has been good, perhaps as great as 95%. These problems, along with logging tools for detecting and measuring casing-length deformations within a few hundredths of a foot per joint [+/ –9 mm/ +/–13 m] were described by Allen in 1969. At that time the system used two or three collar locators (and/or radioactive bullet locators for direct measurement of formation compaction) spaced about one joint length apart. Calculations were made from film recordings made at a scale of 50 to 60 in./100 ft [1.27 to 1.52 m/30.48 m] of hole logged. Subsequently, this equipment has been improved and other investigators have developed at least one alternative system. Statement of the Problem Measurement of subsurface compaction has been a problem in Wilmington field for a number of years and all the older in-situ casing-joint-length investigations were related to this problem. Recently, data requirements for environmental impact reports and studies in both oil and geothermal fields have revived interest in these measurements. In-situ baserun casing-length measurements on new wells have been required in certain instances. Investigations of potential formation compaction in geothermal areas are under way, including government grants for development of measurement systems. Current state-of-the-art tools will be used as a base for developing similar tools that can be used effectively at geothermal reservoir temperatures. To detect small amounts of compaction, by either casing deformation or radioactive bullet displacement, downhole measurements accurate to a few hundredths of a foot [9 mm] or less are necessary. A major problem in this type of logging has always been tool "bounce." Bounce is defined as an erratic tool speed in the hole, caused by drag and cable stretch, while the footage recording device at the surface is recording-at a uniform scale. Obviously, erroneous measurements will be made when this happens. This problem is accentuated when logging older wells wherein scale, corrosion, and tubing wear marks have roughened the pipe interior. Deviated holes, which are common in Wilmington field, also increase bounce. Several other instrument systems have been used in very shallow water wells and in engineering geology applications, but these systems generally are not applicable in a deepwell environment. Tool Development To overcome the bounce problem, a downhole tracking system with small odometer wheels was devised by the City of Long Beach and built by Dresser-Atlas. The tool body is ex-centered by springs that push the wheels into a firm contact with the casing. Two tracking wheels are used, each having five magnets spaced around its periphery. These magnets trigger a reed switch each time passed and a "blip" is recorded at the surface. Each blip records that the tool has traveled about 2 in. [5.1 cm], regardless of the amount of cable that may have emerged from the hole during this same interval. Two wheels are used to provide a redundancy factor; if both are in contact with the hole wall, they should record about the same amount of tool travel (they are not synchronized). Because of occasional lift-off of the casing wall by the upper wheel, resulting from varying cable pull, the lower wheel has proved the most reliable. JPT P. 805^
Presented am results of compaction of 11 unconsolidated, fine- to medium-grained, arkosic sand cores, 1-7/8 in. in diameter and 3 to 4 in. long. Direct measurements of the pore fluid pressure and bulk volume changes of each sample were made as the pore fluids were expelled.At a constant overburden (external) pressure of 3,000 psi and a temperature of 140 degrees F, the calculated bulk volume compressibilities ranged from 7.4 x 10 to 3 x 10 psi, whereas the pore volume compressibilities varied from 10 to 10 psi in the 0 to 3,000 psi effective pressure range. The void ratios in the same effective pressure range varied from 0.85 to 0.19. Compressibility increases with increasing feldspar and clay content. Compressibilities obtained when using hydrostatic loading equipment are 55 to 100 percent higher than those determined when using uniaxial compaction apparatus. Introduction Numerous investigators studied the compressibility of consolidated rocks and unconsolidated sands. The writer conducted compaction tests in a hydrostatic cell on unconsolidated producing oil sands of Pliocene age from the Los Angeles basin, Calif. There is a lack of experimental data on the compressibilities of unconsolidated sands; yet, such sands are the cause of many well completion and producing problems worldwide.The samples tested were taken from a massive sand interval, greater than 100 ft in thickness. This unit is of deep-water origin and was probably deposited by a combination of bottom currents and distant-from-the-source turbidity currents. Some streaks of very coarse-grained sand and gravel occur in the generally fine- to medium-grained massive sand interval.It is very difficult to duplicate actual reservoir conditions in the laboratory because of the various loading conditions that may exist in the reservoir. Possible loading conditions on a hypothetical Possible loading conditions on a hypothetical sediment cube are presented in Fig. 1. The first condition presented (Fig. 1A) is polyaxial loading, in which none of the three principal stresses are equal. Some investigators prefer to call this stress condition triaxial loading. Although this stress condition may represent the subsurface conditions, it is extremely difficult to duplicate in the laboratory. The second possible loading condition (Fig. 1B) is hydrostatic, in which the three principal stresses applied are equal. This type of loading probably exists during the initial stages of deposition and compaction. The third type of loading (Fig. 1C) is triaxial, in which two of the three principal stresses are equal. Although some investigators justifiably refer to it as biaxial stress, the term triaxial is strongly imbedded in the civil engineering and earth sciences literature.In the uniaxial loading condition (Fig. 1D), the applied force acts in one direction only and is perpendicular to one surface of the sample material. perpendicular to one surface of the sample material. The four faces of the cube parallel to the direction of the stress remain stationary. This arrangement can be achieved by placing the sample in a thick-walled, cylindrical chamber, the sides of which are stationary. The pressure can be applied with either one or two pistons, and the change in the volume of the sample is reflected by the change in the length of the sample. In the field of soil mechanics this method is sometimes referred to as triaxial testing. This type of loading is probably approached in an oil reservoir as the reservoir pressure is depleted as a result of production. It pressure is depleted as a result of production. It should be mentioned also that some investigators reserve the term uniaxial for cases when there is a vertical stress, but no lateral restraint and hence no lateral stress. In biaxial loading (Fig. 1E), the two principal stresses are equal, while two faces of the cube are held stationary. GENERAL THEORY OF COMPACTION The total stress within a porous medium is composed of the intergranular stress and the pore fluid stress. The intergranular stress represents the contact forces developed between adjacent particles. particles. SPEJ P. 132
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