Scale is a major problem for the oil and gas industry and is often controlled by the use of downhole scale inhibitor squeeze treatments. The placement of scale inhibitor in acid fractured limestone reservoirs presents a particular challenge and effective placement of scale inhibitor cannot be guaranteed when performing conventional low rate (<10bpm) bullhead squeeze treatments. In order to ensure the fluid package is placed over the whole of fractured interval it is necessary to perform high rate scale squeezes (40–60bpm) in conjunction with mechanical divertors. However, these treatments are expensive and limit the amount to treatments that can be performed per day in a scale squeeze campaign. This paper describes the development of a range of viscosified polymeric scale inhibitors for squeeze application in acid fractured wells. A particular feature of these products is their viscous self diverting nature which means they can be used at low pump rates at rates of <10bpm. This method also precludes the use of mechanical divertors and enables cross flow problems to be overcome and effective chemical placement over the whole of fractured interval. In addition, this offers the benefit of improved scale control and squeeze lifetimes coupled to considerable economic savings by being able to perform more treatments per day using conventional pumping equipment. A detailed investigation into the rheological properties of selected products has been performed to design the optimal delivery system. Experimental data on the compatibility of a variety of viscosifying agents and chemical breakers different types of polymeric scale inhibitors will be presented. This will include viscosity profiles, shear thinning behavior and breaking times for these systems. Inhibitor performance and core flood studies to evaluate formation damage potential and retention and release characteristics will be also be presented. In addition, the paper will add the results of a computer modelling study to validate the experimental data and aid the placement strategy for optimum field application. Introduction Oilfield scale is a key issue in the petroleum industry where vast amounts of water are used and co-produced with hydrocarbons. The formation of mineral scale can create a range of problems including; reduction in pipe carrying capacity, increase in operational hazards due to blocked valves, localization of corrosion attack, impedance of heat transfer, and increases in operating costs due to down time and system maintenance.
Oilfield scale formation is dependent upon the production of water and as a result most scale inhibitors are water soluble and deployed using an aqueous phase. For treatment of wells that produce only small amounts of water and/or have water sensitive matrices and wells with high water cuts with lifting problems the use of an aqueous inhibitor can cause many problems. Even with the development of oil miscible and emulsified scale inhibitors the same problem can be encountered when the incorrect screening procedure has been used in the laboratory. This study describes the development of a range of truly oil soluble scale inhibitors for squeeze application. A particular feature of these materials is that they preclude aqueous phases and are soluble in crude oil and diesels. The products have been designed so that is possible to deploy calcium sensitive scale inhibitors in a non-aqueous medium. Upon contact with formation water passing the near wellbore the scale inhibitor will partition into the water phase and undergo a precipitation reaction. This provides a mechanism for potentially increasing treatment lifetime. In addition, the scale inhibitor precipitation can be further controlled and enhanced through emulsification with a calcium loaded aqueous medium also containing organic additives to aid and enhance the precipitation process. Although this involves incorporating water into the product package the invert emulsion provides an oil continuous matrix and is still considered to be significantly less damaging to water sensitive formations than standard oil dispersible and emulsified scale inhibitor packages. A detailed investigation into the properties of selected oil soluble and emulsified products has been performed. Experimental data on compatibility with production fluids, thermal ageing, oil/water partitioning, inhibitor performance, extent of precipitation and core flood studies to evaluate formation damage potential and retention and release characteristics will be presented. This paper will also highlight how the use of the oil soluble precipitation process can increase squeeze lifetimes when compared to traditional aqueous squeeze treatments. In addition, a new core flood procedure for the screening and evaluation of non-aqueous chemical treatments will be described and the implications this has for field application of these products will be discussed. Introduction Oilfield scale is a key issue in the petroleum industry where vast amounts of water are used and co-produced with hydrocarbons. The formation of mineral scale can create a range of problems including; reduction in pipe carrying capacity, increase in operational hazards due to blocked valves, localization of corrosion attack, impedance of heat transfer, and increases in operating costs due to down time and system maintenance.
The introduction of more stringent environmental regulation within the North Sea has resulted in increased focus on developing environmentally acceptable inhibitors for application to oil and gas applications. One approach in fulfilling these criteria has been the emergence of multifunctional combined products. This paper demonstrates how this approach can be used effectively to control both scale and corrosion problems. A new environmentally friendly product was developed within the laboratory that gave improved scale control performance against conventional products while also affording excellent corrosion control. A series of tests were conducted to establish the performance of the product as well as compatibility with produced fluids from a North Sea platform. The results of the laboratory investigation are discussed in detail including the advantages and disadvantages offered by this approach as well as the potential environmental benefits. Introduction The North Sea is a mature region where continued economically viable oil and gas production has resulted in a number of technical and logistical challenges. Not least of these is extending the life of production wells to maintain hydrocarbon recovery while addressing issues of design life and changing production conditions(1). Two areas of particular importance are corrosion of pipelines and the topside facilities and the formation of mineral scale due to the large amounts of water used and co-produced with hydrocarbons(2,3). Carbon steel is extensively used in the petroleum industry for both pipelines to transport the hydrocarbons to shore for processing and in the offshore topside facilities. This grade of steel has an inherently low resistance to corrosion, but due to the potential Capex savings and other associated economic issues, is the material most commonly utilised. However, oil and gas production is accompanied by a number of potentially corrosive environmental factors including differing amounts of water with varying concentrations and types of salt, CO2, H2S, organic acids, as well as liquid hydrocarbons(4). These factors combine to give rise to a particularly aggressive environment, where corrosion can be rapid and severe. A review of the literature yields numerous cases of corrosion failures with the associated loss in production and revenue this can cause(5,6). A further concern, most notable in the North Sea, is the problems encountered in production due to the formation and build up of scale(7). As the water cut in mature fields increases and greater quantities of seawater are re-injected to maintain reservoir pressure so the problems of scale formation increase. This can lead to blockages in valves and a steady reduction in the pipe carrying capacity. This can eventually result in full suspension of production while essential maintenance is conducted which is an extremely costly exercise. The formation of scale can also influence localized corrosion depending on the nature and type of scale formed and several other factors including, pH, pressure and temperature(8). The majority of producing wells where scale formation is an issue are treated by chemical means(9). A range of scale inhibitors have been developed over the years with particular physical and chemical properties developed for specific field applications(10). This type of chemical solution is also widely utilized in corrosion control, and like scale inhibitors, are designed to be system specific. These offer the benefit of being relatively inexpensive compared to corrosion resistant alloys (CRA's) while allowing the design life of the facility to be extended.
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