A combination of known crosslinked gel chemistry with careful problem diagnosis, wellbore and formation temperature modeling, and zone isolation techniques yields a high success rate for shutting off unwanted gas influx into production wells in the Prudhoe Bay Field of Alaska. The paper includes candidate selection criteria, methodology of temperature simulation, job design, field operations case histories, and pre- and post-job production data for evaluation of success. This approach has led to a 60% technical success rate, primarily on wells that had cement squeeze failures. Job costs are about 75% those of comparable cement squeezes.
Patient specific implants are becoming viable treatment options in some orthopaedic applications through advances in additive manufacturing and 3D printing techniques. One potential application is for treatment of segmental bone defects, particularly in patients suffering from bone cancer. Current treatment options are: Amputation, megaprosthesis, or allografts. These treatments are often highly invasive, may require a partial/full joint replacement and are limited by mechanical properties, which affect the life of the implant. The Ti6Al4V implant proposed in this research was designed to fit a mid-diaphyseal segmental bone defect, mimic the mechanical properties of bone, facilitate osseointegration and reduce wear at the bone-implant surface. Computer-Aided Designs (CAD) were constructed of patient-specific Ti6Al4V implants based off the geometry of (1) a patient suffering from a lesion on the mid-diaphysis of the femur and, (2) a 4th Generation right Sawbones® femur. Pore size and shape were assessed using Finite Element Analyses (FEA) software. The overall porosity was maximized to develop an implant with an effective elastic modulus equivalent to bone. The two implants were then fabricated using Direct Metal Laser Sintering (DMLS). The geometry of the physical implant was measured and mechanically loaded under compression to validate the computational model. FEA was an effective tool for optimizing the pore size, shape and overall porosity of the implant, which indicated that 1mm circular pores in three orthogonal planes at an overall porosity of 54-76% would produce an implant with an effective elastic modulus equivalent to cortical bone. Geometric analysis of the 3D printed implant indicated the pore sizes were reduced by an average of 16% as compared to the computational model and that there was a correlation between the size and precision of the pore and the orientation of the implant during the additive build. Compression testing of the implants indicated that they had an effective elastic modulus of 20.8 and 10.5 GPa, which is within the accepted values for cortical bone.
Selective shutoff of undesired water influx by nonselective (fullbore) placement of treating chemicals has been successfully demonstrated in production wells of the Prudhoe Bay field. This was accomplished through:careful choice of candidates with known high conductivity water influx pathways (fault, hydraulic fracture, thief),placement that exploited conductivity differences without zonal isolation, anduse of established polymer gel chemistry with previously demonstrated ability to shut off water preferentially to oil. INTRODUCTION Waterflooding at Prudhoe Bay was initiated in 1983. Currently there are more than 160 water or water-alternating. gas injection wells in operation, supporting, in inverted nine-spot patterns, 480-plus producers. Due to waterflood maturity, a significant number of producers have watercuts of 90% or higher. While most of the water produced is necessary for oil recovery, there are a number of occurrences of influx from watered-out zones or from the underlying Sadlerochit aquifer that contribute to water cut, but not to oil production. Wellbore treatments with cement (coiled tubing perforation squeezes) have been successfully used to shut off unwanted water influx from cement channels or from hydraulically isolated zones in unfractured production wells.1,2 Similar treatments have been employed to delay coning from bottom water caused by movement of water-oil-contact. However, wellbore shutoff has been only partially successful at controlling water influx from offending zones that are not hydraulically isolated from desired producing intervals. Furthermore, in cases where influx is via a segment of a hydraulic fracture that has inadvertently penetrated a water zone, a wellbore treatment is not expected to have much, if any, effect on water cut, without sacrifice of the entire fracture's connectivity to the wellbore, with corresponding loss of oil rate.
The paper describes laboratory development and field application of polymer-stabilized foams for gas-control in Prudhoe Bay field, including formulation of the foam, its evaluation in sand-packs, and treatments of several wells at Prudhoe Bay. It will also document long term reduction of excessive GOR (gas-oil-ratio) in hydraulically fractured wells with small impact on black oil production. Candidate selection criteria, treatment design/implementation and three case histories (with summaries of all treatments to date) will be covered along with future enhancements to treatment design. Introduction Facility constraints on handling excessive gas production have limited black oil rates at Prudhoe Bay field for a number of years. Approaches to dealing with this problem have included expansion of gas handling facilities, so that current capacity is approximately 7.5 BSCF/day. Gas-cap expansion with continuing production, cusping (shale under-runs), and propped hydraulic fractures that grow upward into a gassed-out region or close enough to the gas-oil-contact (GOC) to cause coning, continue to increase field-wide gas-oil-ratio (GOR), with concomitant negative impact on liquid rates. Increasing standoff from encroaching GOC and zone shutoff of gas cusping have been addressed with remarkable success using both cement and cross-linked polymer-gel recompletions. Attempts to use foam to address gas coning associated with GOC encroachment met with limited technical success. The short-lived treatments were judged uneconomic and were discontinued. Prior to work described in this paper, the only attempts to control excessive gas production from high GOR hydraulically fractured wells involved cyclic production or simply shutting in the well or, in some cases, side-tracking. Inability to isolate the offending zone is a major reason gas shut-off re-completions were not attempted in fractured wells. Three technical developments led us to re-evaluate the use of foam for gas shut-off. First, theoretical work on critical rates for water- and gas coning has given important insight into the types of candidates most amenable to treatment for coning problems. To briefly summarize, effective treatment of a typical matrix coning problem requires a blocking agent that extends radially many tens to hundreds of feet from the wellbore, a technically and economically daunting requirement. However, coning induced by a highly conductive vertical fracture can be controlled by sealing off the fracture/gas-zone connectivity. This can be accomplished by plugging the fracture itself, or by placing a blocking agent in matrix between the fracture and the gas source. Treatment volume for effective gas shutoff is expected to thus be much smaller/more economical than that required to treat a matrix problem. Furthermore, correction of a matrix coning problem is expected to increase the critical production rate prior to reoccurrence of coning by 1.5 to 5 fold, whereas correction of a fracture connection to unwanted fluid can result in an order of magnitude or more increase in the critical rate. Second, surfactants that produce an aqueous-phase foam with stability to oil saturations approaching 30-35% (based on our laboratory studies) have become available. This offers the possibility to employ indiscriminate placement of foam or foaming agent, while relying on higher oil saturations to destabilize foam that invades an oil producing interval. Third, adding appropriate water-soluble polymers has been shown to increase foam stability and strength. In addition, utilization of a polymer with cross-linkable functionality offers the further option of forming an even stronger gelled foam. These options offered the possibility of increasing treatment lifetime, and hence economics, through use of a stronger foam than had been previously available. With these advancements we believed it was now possible to attack the problem of excessive gas influx from matrix into a propped hydraulic fracture. P. 443
The methods usually employed for the histological processing of orthopaedic specimens of cemented joint arthroplasties involve treatment with methacrylate monomer and organic solvents which dissolve the polymethylmethacrylate cement. This may distort the intimate relationship of the cell layers along the surface of the interface between the bone and the cemented implant. The authors report on a technique for the processing and embedding of cemented orthopaedic implants which permits preservation of the polymethylmethacrylate cement. The method utilizes a modification of Spurr's low viscosity epoxy resin and avoids the use of solvents such as acetone. Undecalcified sections of cemented joint replacements from animal studies and human specimens have been prepared using this method. It is possible to use these sections for detailed histomorphologic and histomorphometric analysis of bone tissue and of the soft tissue membrane adjacent to the polymethylmethacrylate cement.
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