Appropriate utilization of clinical laboratory services is important for patient care and requires institutional stewardship. Clinical laboratory stewardship programs are dedicated to improving the ordering, retrieval, and interpretation of appropriate laboratory tests. In addition, these programs focus on developing, maintaining, and improving systems to provide proper financial coverage for medically necessary testing. Overall, clinical laboratory stewardship programs help clinicians improve the quality of patient care while reducing costs to patients, hospitals, and health systems. This document, which was created by a new multiinstitutional committee interested in promoting and formalizing laboratory stewardship, summarizes core elements of successful hospital-based clinical laboratory stewardship programs. The core elements will also be helpful for independent commercial clinical laboratories.
Proposal Described are proof-of-concept developments to form a seal for mitigating sustained casing pressure caused by annular pressure buildup. Annular pressure can result from numerous sources, including tubing leaks, loss of isolation potential within the cement column because of poor mud displacement, free water-induced channels, stress fractures, and failure of the cement to cover all potential sources of annular pressure. In most cases, annular pressure is not observed at the wellhead until the well is placed on production, making it difficult to identify, access, or remediate the pressure source. A new and novel approach to remediation has been tested in which a low-melt-point alloy metal is dropped down the backside of the casing where annular pressure has been observed. The metal is allowed to accumulate at the top of cement or other physical barrier, melted with an induction-heating tool, and allowed to cool and solidify. This process forms an annular seal to stop fluid communication between the formation and wellhead. This method was demonstrated within a full-scale, simulated well section. An electromagnetic induction tool provided sufficient localized heating to completely melt solder-type alloy metal placed between concentric casings. Subsequent pressure-testing verified that a complete melt, sufficient to provide an effective seal against fluid pressure, was achieved in both water- and synthetic-based drilling fluids. Shear-bond test results of various alloys were equal or superior to cement, and the solid-liquid phase transitions (set points) occurred at precise temperature levels. All metals tested contained bismuth because of its unique characteristic of expanding upon solidification to provide enhanced pressure-containment performance. Full-scale testing was conducted using 17-ft long concentric annular models constructed of 8-in. and 5-in. diameter steel pipes. Subsequent field-testing is currently being planned. Introduction This paper summarizes experimental efforts to form an annular seal for the purpose of mitigating sustained casing pressure, or annular gas pressure buildup. Annular pressure can result from numerous sources such as tubing leaks, loss of isolation potential within the cement column caused by poor mud displacement, free water- induced channels, stress fractures, or failure of the cement to cover all potential sources of annular pressure. In most cases, annular pressure is not observed at the wellhead until after the well is placed on production, making it difficult to resolve the matter, i.e., isolate the zone from which formation fluid communication is taking place. There is seldom a feasible means of physically reaching any of the key points of fluid communication after the occurrence has been observed. Past efforts to remediate have been compromised by failure to reach deeply into the annulus and by chemical contamination of the remedial sealant. The proposed method drops a low-melt-point alloy metal down the backside of the casing where annular pressure has been observed. The metal is then melted by an innovative heating process and allowed to cool and solidify. The intent is to form an annular seal to stop fluid communication between the rock formation and the wellhead as deeply within the annulus as physically possible. This concept was tested using a commercial tool developed for use in artificial lift that produces heat at select locations by electromagnetic induction. The tests described are also intended to determine whether this tool has application for the purpose described. Background A major purpose of primary cementing is to form a permanent seal between the borehole wall and the casing run into it. Total success in this effort implies that all nonproduced formation fluids remain in their respective formations for the entire productive and post-abandonment life of the well. Sustained casing pressure (SCP) detected on the backside of the casing can be an indication of fluid or gas movement within the annulus. This movement can result from failed or insufficient cement coverage, communication through tubular connections and seals, or thermal expansion of fluids in a confined space during production operations. This discussion will focus on remediation of fluid movement or communication.
Annular gas pressure, also known as sustained casing pressure (SCP), is a common problem and potential threat to the safety of personnel and equipment, as well as to the environment. Improved means of primary cementation and life-of-the-well simulations show promise for preventing future annular gas-flow problems. However, there has been little success in eliminating SCP, once developed, without jeopardizing the economic life of a well. Possible solutions to SCP in the form of remediation include bullheading cement, injection of zinc bromide brines into the well's annulus, or use of expensive resins to seal the annulus. A proposed solution that can compensate for the drawbacks of the above options and has shown promise on small-scale physical models is palletized alloy-metal. This solution involves placing palletized alloy-metal into the well's annulus, heating the alloymetal above its melting point, and then allowing the alloy-metal to cool. These steps form a continuous alloy-metal plug in the well's annulus. Data and conclusions documented in this paper are from full-scale pipe-in-pipe and pipe-in-sandstone geometry models having the following scope:Geometry of 5 1/2×8 1/2-in. pipe-in-sandstone and 10 3/4×13 3/8-in. pipe-in-pipe configurationsModel length limited to 15 ft and deviated at 30° from verticalAlloy-metal pellets placed and activated with water-based drilling fluid present in annuliTemperature limited to 200°F Results are also documented by dissecting the models and photographing the exposed cross-sections. Information gathered in this testing will help with the field introduction of this technology. Introduction SCP is a growing problem among offshore wells, leading to expensive shut-ins and remediations on many wells. Poor primary cementing, inadequate cement coverage, gas/water influx during or after cement placement, mud-cake shrinkage, and the development of stress-induced microfractures and microannuli are all cited as potential factors in SCP. The time between well completion and the onset of SCP can indicate the more likely causes. While there are several suspected culprits for SCP, pressure and temperature cycles are high on the list. Casing growth and contraction that result from production cycles and stimulation operations can de-couple the bond between the cement and casing. These forces can also stress-crack the cement. Both scenarios can create small pathways for high-pressure, lowvolume communication of annular gas to the surface, but the inaccessible nature of these pathways limits remediation options. Early onset mechanisms can include the following:Gas-cutting of the cementGas movement through a free-water channelCasing/tubing connection leaksInadequate cement coverage Late onset SCP can result from the following:Channels of bypassed mudStress cracks in the annular cement sheathShrinking or drying of the mud filter-cakeCasing/tubing connection leaks These factors are well documented, appearing frequently in past research. The following sections summarize a few main causes.
In deepwater or other sub-sea completed wells, fluids, usually spacers or drilling fluid, are commonly trapped in casing annuli above the top-of-cement and below the wellhead. When these trapped fluids are heated by the passage of warm produced fluids, thermal expansion can create very high pressures (10,000 -12,000 psi or more) and cause the collapse of casing and tubing strings. 1,2,4,12,15 Mitigation methods such as vacuum insulated tubing to limit heat transfer, 6,7,14 nitrogen-based foam spacers to give highly compressible trapped fluids, 8,9,10,11 crushable urethane foam, 3 etc. are somewhat successful but are either very expensive, logistically troublesome or have unacceptable failure rates. This paper continues the discussion of a new approach which has created a water-based spacer fluid that will be used just ahead of the cement. The spacer contains perhaps 10-30% of emulsified liquid methyl methacrylate monomer (MMA). Upon polymerization, the MMA phase shrinks by 20%, creating room for the remaining fluid to thermally expand without creating catastrophic pressure. The polymerization is triggered by heat and a chemical initiator. The target temperature can be controlled by choosing an appropriate type and concentration of chemical initiator. Premature polymerization during spacer placement can be prevented by an appropriate type, and amount, of inhibitor. The initial lab work and a mid-scale field trial of this technology were reported in detail in SPE/IADC 104698. 1 This paper covers the development and field testing (land) of all the equipment and processes necessary to apply the technology in deep water.
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