Drill-stem testing (DST) has been used for many years in the oilfield to establish reliable reservoir characterization. The DST data are used to provide estimated production, fluid analysis, and to help design the final completion and production facilities.More recently, discoveries in abnormal pressure gradients and deep formations have not only pushed the capabilities of traditional equipment and procedures, but also increased the safety hazards inherent to DST operations. At surface, high pressures, the presence of H 2 S, and toxic well fluids increase the difficulty in deployment of real-time data acquisition and sampling equipment via wireline. Downhole, the high hydrostatic pressures normally found in deep environments can hinder the operation of the downhole tools. Often, to achieve high hydrostatic pressures, the operator is forced to use drilling muds which may have very low pressure transmissibility and solids problems that interfere with annulus-pressure/pulse-response tools.The need to improve the quality of information gathered during DSTs in hostile environments has driven a major oilfield engineering company to research concepts that could improve capabilities of traditional DST systems.This research led to the development of a novel telemetry system that uses acoustic bi-directional acoustic transmission through the tubing string. This system, compact and easy to deploy into the well, provides real-time data-acquisition flexibility in various depths in the string, enabling the constant monitoring of the wellbore conditions throughout the DST. It's design, applications, and ability to simplify job procedures, reduce risks, and improve quality of information when linked to data acquisition and tool operation, will be the focus of this paper.This new system provides greater efficiency in acquiring data in deeper, high-pressure DST environments than are currently possible with the standard methods.
The oilfield industry classifies wells with bottomhole temperatures in excess of 300°F as high-temperature (HT) wellbores. Because they usually can produce large hydrocarbon volumes, all attempts to develop and produce these areas have been tried, although prospects with HT conditions present more challenging conditions. These challenges affect operational planning, equipment applications, engineering job design, and execution, and proper planning is critical to achieving job objectives. This paper presents lessons learned and equipment applications in HT well testing environments globally, where different reservoir scenarios require modificarions to procedures, equipment configuration, and safety requirements. Each job requires consideration of ambient environmental criteria in addition to the individual operator's testing policies. Therefore, different methods for achieving job goals are needed. The lessons learned will be applicable to current scenarios in many areas and will be discussed to allow the operators to determine proper testing procedures for their HT jobs in similar conditions. Well tests are performed using different downhole tools and procedures. A summary of these topics will include: Operational advantages and efficiency gains New technologies to make well testing operations and evaluations more accurate Collection of downhole samples in (pressure, volume, temperature (PVT) conditions to provide the most appropriate data to be considered during future development of prospect. New technologies are an excellent example of how technical developments and advances in the oil industry (gauges, downhole equipment, samplers, etc.) have been applied to operations in the oilfield to improve the decision-making capabilities in the oil and gas industry as well as increase well-testing evaluation success, even in extreme and challenging environments. These enhancements allow improved economic and operational efficiency as well as better safety conditions, both for the involved personnel and the environment during testing operations.
Well testing generates essential reservoir data, and although it can impact initial operating expenditures significantly in oil or gas upstream projects, the data generated can be essential to the efficiency of the completion operation ultimately designed. While having proven its value, data-gathering methods still must be balanced with operational and economic strategies, if the completion goals are to be economically feasible. Drill-Stem Test (DST) tools with downhole shut in and memory gauges are commonly used in well testing operations to provide reliable data and enhance operational efficiency of the completion. However, DST tools alone cannot monitor reservoir pressure response in real-time for justifying the subsequent operational objective changes during the data acquisition, because the recorded data cannot be retrieved at surface until the well test operation is completed, and the workstring is pulled out of hole. To overcome this problem, surface read-out (SRO) systems can be used with DST for retrieving downhole memory-gauge data in real time; thus, the pressure response can be monitored directly, and operational changes can be made immediately, based on actual reservoir conditions. An SRO system was used in Senoro-6 well to aid in justifying a shut-in duration to reach reservoir boundary and attain information that indicated the need for a stimulation treatment. Based on the real-time SRO data, it was found out that the permeability was lower than expected, and shut-in should be terminated earlier than planned, since the required shut-in time to reach boundary would be much longer than anticipated. Prolonging testing time would not be reasonable when reviewing operational and economic considerations. In addition, pressure transient analysis from real time SRO data indicated that the well had severe wellbore damage. Thus, the decision was made to conduct matrix acid stimulation based on the SRO data and to continue with post-stimulation well testing without pulling the DST string out of the hole. Post-test results showed a 22% production improvement, while the operation itself saved more than US$150,000 from daily rig cost. This approach in using the SRO system proved to be effective in helping to determine an efficient testing operation and completion strategy.
A leading exploration and production company in India drilled a high-pressure/high-temperature (HP/HT) well in eastern offshore India and required drillstem testing (DST) to be conducted using the service company's multiple-set HP/HT retrievable packer, multicycle circulating valve, and multicycle tester valve. The bottomhole temperature at reservoir depth was approximately 460°F. This case study discusses the recently conducted DST of the HP/HT well by one of the largest global oilfield service providers in collaboration with the operator. The HP/HT environment presented many challenges. The operator initially decided to deploy a permanent packer; however, after comprehensive preoperation planning with the service provider, the decision was made to run a retrievable packer to save time and costs associated with setting and milling/retrieving a permanent packer. The hook-wall concentric bypass, 7-in. retrievable packer was designed and tested for HP/HT environments. It was decided to deploy a full-suite multicycle DST tool string rated to 450°F. To help ensure a higher success rate for the long duration of the test, a clear fluid system of lower weight (14.6 lbm/gal) was used for reliable functioning of the annulus pressure-operated DST tools after a hermetical test and heavy kill mud (15.7 lbm/gal) was used for the well kill operation. Deploying a full suite of annulus pressure-operated, multicycle DST string rated for HP/HT conditions permitted the testing of the well to be performed safely and efficiently without any breach to safety and service quality. The initial cleanup, three-bean study, and downhole buildup were successfully completed. Temperature recorded in this well at the 7-in. retrievable packer depth was 436°F, and the reservoir temperature was extrapolated to approximately 460°F. The reservoir was successfully tested with an annulus pressure-operated multicycle DST string designed to withstand the challenging HP/HT environment. The operation set a new global record, which is the highest recorded bottomhole temperature during DST using the service company's retrievable packer and multicycle DST tools.
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