Summary The success of a scale inhibitor treatment depends on placement efficiency. The scale inhibitor should be placed so that all water-producing intervals accept a sufficient quantity of the total treatment volume. If significant permeability or pressure variations are present in the interval to be treated, treatment fluid will enter the zones with the higher permeability and lower pressure, leaving little fluid to treat the other zones, which can be the water- producing zones. The challenge is even greater in long, horizontal wells with significant permeability and pressure contrast. To achieve a more uniform fluid coverage, the original flow distribution across intervals often needs to be altered. The methods used to alter this are called "diversion" methods. The purpose is to divert the flow from one portion of the interval to another. In response to this challenge, a joint study with the objective of improving the placement of treatment fluids was initiated by a major operator in the North Sea and two service companies in 2002. The joint work resulted in development of a fully viscosified scale inhibitor system. The system comprises a purified xanthan viscosifying agent, a standard scale inhibitor for downhole scale squeezing, and a breaker to achieve controlled gel breaking down hole. The system has been field tested at Norne field in two long horizontal wells and at Heidrun field in one long deviated well, all with significant permeability variations and crossflow. The operations were successful and the scale treatments have protected the wells from scaling. This paper describes the product qualification process, placement simulation, temperature prediction, gel breaking characteristics, case histories, and post-job evaluation.
Summary Scale inhibitor squeeze treatments have regularly been conducted to prevent both sulphate and carbonate scale depositions in a specific North Sea field for more than 10 years. However, some wells, in which the fluid is producing from the "clean" sandstone formation, have experienced relatively short squeeze lives, when squeezing a conventional phosphonate scale inhibitor treatment. A research program has been conducted to develop a novel polymer scale inhibitor chemistry, which combines performance in a number of laboratory static and dynamic tests, with improved scale inhibitor adsorption properties on "clean" sandstone formations. Field trials have also been conducted with satisfactory results. This paper outlines the concept of how novel scale inhibitor chemistry was developed by incorporating a special monomer to make the final copolymer scale inhibitor. The monomer was introduced to enhance the inhibitor adsorption properties, because it carries a special functional group to improve the scale inhibitor affinity for the reservoir rock. This special functional group plays a key role for the newly developed scale inhibitor, to give improved and acceptable squeeze lives. A critical aspect of the program included optimizing the monomer content to achieve a good adsorption/desorption balance, to ensure that the scale inhibitor would be desorbed/released from the reservoir rock to meet the requirements of an acceptable squeeze program. An added bonus was that the environmental properties of the scale inhibitor polymer were also improved because of the introduction of the special monomer. A number of beaker and dynamic loop tests were conducted and the inhibitor showed an excellent efficiency in both sulphate and carbonate scale inhibition performance tests under the test conditions adopted. This paper also presents detailed laboratory and field data; the treatment design strategy and deployment method adopted for the scale inhibitor.
Logging While Tripping (LWT) is a recent development in formation evaluation technology that provides a means by which open hole logs are obtained more quickly and with less risk than is currently possible using conventional wireline or measurement-while-drilling techniques. LWT Services Inc., a Calgary based company, has developed this new approach to the logging process which involves using specially modified drill collars and memory-based logging tools positioned within the drillstring to record log data as drillpipe is tripped out of the well. LWT tools are deployed and retrieved from the drillstring only when log data is required. After the data is acquired and the tools retrieved from the well, casing can be run without an additional hole-conditioning trip, saving considerable rig time. Risk is minimized because logging tools are not exposed to the open wellbore, but stay protected inside the drillstring. Service quality is reviewed by showing examples dealing with data quality and depth control. While LWT's compensated neutron provides an open hole quality measurement, some correction is needed to provide absolute porosity values in varying borehole sizes. Depth control examples compare favourably to wireline conveyed logs with an accuracy approaching +/- 1 m per 3,000 m of total depth. A few applications for this new technology are anticipated to be:Horizontal wells which are currently not evaluated due to the prohibitive cost and risk associated with pipe conveyed and MWD/LWD systemsReconnaissance logging, done at any time throughout the drilling of the well, will enable geologists to identify zones and monitor well trajectoryUnderbalanced, air-drilled wells can be logged as they are drilled, thereby eliminating the need to run open hole logs under pressure. Presently, LWT Services Inc. is working on a prototype 1 11/16 in. induction tool. In order to make induction measurements from inside the drillstring, a nonconductive composite drill collar has been constructed, tested, and successfully drilled 850 ft. in a test well in Oklahoma. Another development includes a compensated photoelectric density tool. Background Logging While Tripping (LWT) represents a new approach in the process of open hole data acquisition. LWT makes use of memory-based logging tools positioned in the drillstring to record data as drill pipe is tripped out of the well. Unlike measurement-while-drilling tools, LWT tools are not a permanent part of the drillstring but instead are deployed and retrieved from the drillstring only when log data is required. Currently, LWT provides FIGURE 1: LWT operation. (Available in full paper) compensated neutron and gamma ray services while the dual induction and photoelectric density are under development. While in its early stages of development, LWT's technology is aimed at providing drillers with significant cost savings in the area of open hole data acquisition. These cost savings will be realized in two principal areas:Decrease in rig time for the logging process and,Decrease in risk of tool loss or damage downhole. This paper presents an overview of LWT's operation, service quality, and applications supported by several examples. In closing, a brief review of future prospects is presented.
The success of a scale inhibitor treatment depends on the placement efficiency. The scale inhibitor should be placed so that all water producing intervals accept a sufficient quantity of the total treatment volume. If significant permeability or pressure variations are present in the interval to be treated, treatment fluid will enter the zones with the higher permeability and lower pressure leaving little fluid to treat the other zones, which can be potentially the water producing zones. The challenge is even greater in long horizontal wells with significant permeability and pressure contrast. To achieve a more uniform fluid coverage, the original flow distribution across interval often needs to be altered. The methods used to alter this are called "diversion" methods. The purpose is to divert the flow from one portion of the interval to another. In response to this challenge, a joint study with the objective of improving the placement of treatment fluids was initiated by a major operator in the North Sea and two service companies in 2002. As a result of this work a fully viscosified scale inhibitor system is developed. The system comprises a purified xanthan viscosifying agent, a standard scale inhibitor for downhole scale squeezing and a breaker to achieve controlled gel breaking down hole. The system has been field tested at Norne field in two long horizontal wells at Heidrun field in one long deviated well, all with significant permeability variations and cross flow. The operations were successful and the scale treatments have protected the wells from scaling. The paper describes the product qualification process, placement simulation, temperature prediction and gel breaking characteristics, case histories and post job evaluation. Introduction Both Norne and Heidrun fields have placement challenges regarding scale protection of long horizontal wells. Often these wells have significant permeability and pressure variations along the well bore. Norne is a sub-sea field with a combined production and storage vessel, FPSO (Floating Production, Storage and Offtake) connected to 14 production and 8 sea water injection wells from 6 sub-sea templates. Hence, all major well operations need to be performed using rig or intervention vessel. Well operations are therefore limited by access to rig/vessel and by weather conditions. The field is located at the Haltenbanken area 200 km offshore Mid-Norway and north of the 66th parallel (Fig. 1).
The success of chemical treatments to prevent or remove formation damage, depend on the placement efficiency. In down-hole scale control treatments, diversion techniques are applied for improved placement of scale dissolvers or scale inhibitors in the potentially productive intervals. Foamed scale treatment is a new diversion technology developed by the operator and two oil service companies. The new approach is to foam the scale inhibitor and scale dissolver solutions for improved placement of down-hole scale inhibitor squeezes and scale dissolver treatments. An additional benefit is that the gas used to create foam is perfectly suited for wells with low reservoir pressure and with no gas lift system in place. In theory the foamed fluid will enter the highly injective zones at a higher rate than the others so that the resistance to flow increases in the zones which have accepted the foamed fluid.The technical qualification of the foamed scale chemicals was divided into advanced bottle tests and dynamic flooding tests. The first ever field application was performed in a Norne subsea well, under challenging weather conditions from an intervention vessel. Two subsequent pumping operations; one foamed scale dissolver and one foamed scale inhibitor operation were done. The post job evaluation concluded that the foamed scale treatments were successful and the technology is qualified for future use at the Norne field. The well became protected against scaling as seen from the scale inhibitor return curve, and the well came easily on stream following each treatment. The operational challenges were mostly in connection with wave height and vessel movement affecting the Nitrogen pumping stability.The benefits seen with this technology are: it is a solid free system, it can be deployed by bullheading, the foaming agent is environmentally friendly and the system helps a quick post treatment production.
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