Producing more oil, but with less input power consumption challenges all E&P companies as they pursue sustainable energy resources. The innovative gaslift technique makes surmounting this challenge possible. The conventional gaslift well system has long been in use worldwide, but the design itself results in depth limiting of the lifting capability. Locating the side pocket mandrel just above the packer, where the gaslift valve is installed, as deep as possible is a well-known design. This might not be significant for short pay zone intervals with higher reservoir pressures, but, clearly, constraints arise in long true vertical perforation intervals with lower reservoir pressures. A new gaslift well design has been developed and studied by the PTTEP Well Engineering Team under the Company's "DeepLift" Project. This design has proven to be suitable for use in many types of wells, particularly those containing long true vertical perforation intervals. This new design was granted, by the U.S. Patent and Trademark Office, Patent No. 7,770,637 B2, on August 10 th , 2010. The design comprises a single completion using the same tubing for producing hydrocarbons and delivering gaslift. The top section of the tubing targets producing hydrocarbons while the bottom section aims at delivering gaslift down to the wellbore. Gaslift flows through the perforated tube above the secondary port of the dual-packer, and then through bypass packer downward via a modified bypass string connected to the lower tubing section. Gaslift is injected out of the bottom side pocket mandrel via reverse gaslift valve to the wellbore, approximately at the bottommost perforation intervals, to improve outflow by decreasing the hydrostatic column or increasing the drawdown pressure. Wells that contained 500 -600 mTVD, which is a significant long distance between the top and the bottom perforation depth, were selected for a field trial. An enormous percentage of production gain is due to genuine higher drawdown pressure improvement from 150 psi to 300 psi. This results in a significant production improvement, which is the primary discussion of this paper.
The word "integrity", is defined as: "the state of being whole, complete and entire, in an undiminished or unbroken condition". Well Integrity Remediation, therefore, is maintenance of well quality to insure such totality and undiminished condition.Well integrity has received a significant attention these days, from well conception to well abandonment. The driving factors such as the high oil price along with new techniques for Enhanced Oil Recovery (EOR) make it feasible and profitable to prolong the field life beyond original design. However, an extended well life has led to a higher probability of well integrity related problems e.g. Fatigue, Erosion and Corrosion.As case in point, PTTEP S1 -Sirikit Oilfield, experiences unavoidable well integrity problems, primarily relating to corroded casing due to water encroachment. In this respect, it is the sub-surface challenge to minimize the shut-in time and prolong overall well life. To address these problems, swelling elastomer was considered for a remediation work by isolating leak casing from production system, and thereby preventing further well integrity failure. Properties of inherent elastomeric substances is designed such that, when in contact with the wellbore fluid, will react and swell against the contacted surface providing long-term isolation with no mechanical intervention. The known product e.g. Swellable Packer has been proven for many years mainly for open-hole applications, until such a time as cased-hole remediation techniques are implemented by PTTEP.This paper examines case histories and demonstrates the practicality of Swellable Packer in the cased hole application which aging casings wall were chronically corroded by water encroachment. Two different types of wells: producer and injector, which casing confirmed failure by Production Logging tool (PLT) and Ultra Sonic Imager tool (USIT), were selected as candidates. The background, operation sequence and performance evaluation methodology are detailed on the following sections in this paper.
In the onshore field in the Northern part of Thailand, the wells are typically produced with gas lift and converted to beam pump later, using the annulus space for gas separation. In the past, the completion string must be replaced to switch to beam pumps. However, with the new Hybrid completion, the existing completion can be used, and the amount of workover is reduced. In the new Hybrid completion, two sliding sleeves are installed in the tubing string, allowing us to utilize both artificial lift methods without replacing the tubing. To produce the well with gas lift, both sleeves are closed, and the well is produced normally. When converting the well to be produced with a beam pump, both sliding sleeves are opened, a plug is set above the lower sleeve, and a downhole pump installed above the upper sleeve. This forces the wellbore fluid to flow out to the annulus through the lower sleeve. Since the liquid level is higher than the upper sleeve, most of the gas travels up the annulus while the liquid traverses through the upper sleeve from the annulus into the tubing. The liquid is then pumped along the string with a beam pump. This method acts as a gas separation mechanism to prevent gas lock and reduce efficiency problems for beam pumps. The flexibility to switch between the two artificial lift methods allows us to handle the dynamic wellbore and reservoir conditions more efficiently. The Hybrid completion has enabled us to (1) handle a wider well productivity range, (2) significantly lower the cost of workover, (3) decrease the hazards exposure during operations, and (4) produce oil and gas faster, favoring the economic return.
Success towards waterflood optimization requires the accessibility of downhole contribution and injection, challenging on the conventional cased-hole multi-zone completion where contribution and injection are gathering through sliding sleeve. This paper will describe the success in defining flow profile behind tubing by utilizing Temperature and Spectral Noise Logging. With response in frequency and noise power when fluid flowing through completion accessories, perforation tunnels and porous media, fluid entry points for producer and water departure point can be located by noise logging. Additionally, conventional temperature logging can usually define degree of intake and outflow along with change in fluid phase as a result of change in temperature. In combination of these implications, downhole flow contribution and injection profile can certainly be determined even though fluid moving in and out through production tubing and casing. Regarding pilot field implemtation in Sirikit field, two multi-zone-completed candidates have been selected, operations were carried-out for producer and injector according to the programs individually designed including logging across perforation intervals and station stops for multi-rate flow, transient and shut-in periods. Longer well stabilization is necessary for injector. In addition to production/injection logging interpretation by incorporating pressure, temperature, density and spinner data, the temperature simulation model is generated to determine downhole flowing/injecting contribution with parameters acquired during logging, for example, pressure and temperature. The other reservoir and fluid properties, e.g. permeability, thickness, hydrocarbon saturation, skin, heat conductivity and capacity have been analog based on available data from neighboring areas. Therefore, the historical data on production and injection including nearby well performance may be crucial to define necessary input to the model. In association with the interpretation of noise logging which is utilized in locating contributing/injecting zones, the interpretation strongly relies on acquired temperature data and outputs of temperature simulation model to match with measured temperature profile. However, limitations have been documented when dealing with multi-phase flow, especially in low flow rate condition – considered 5 BPD as a threshold. Sensitivity run with associated paramenters in the interpretation can significantly reduce the number of uncertainties to match with measured temperature profile. Temperature and Spectral Noise Logging to provide input to temperature model can definitely help accessing downhole injection profile for the injector by taking benefit of one phase injecting and having contrast between injecting fluid and geothermal temperatures. This application can significantly improve the waterflood performance and optimization particularly in high vertical heterogeneous reservoirs – thief zones can be identified and shut-off consequently. However, defining downhole contribution for low-rate oil wells producing from multi-layered depleted reservoirs especially in undersaturated condition is still a challenge.
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