Distributed temperature sensing (DTS) is a fiber-optic technology that provides continuous temperature profiles along the length of a well. When placing the fiber inside a coiled tubing (CT), one can monitor the temperature evolution while pumping as well as during a shut-in period. This evolution, in turn, yields some indications about the fluid-placement performance or zonal coverage. So far, interpretation of such DTS traces has been mostly qualitative. The work presented here demonstrates how DTS data can be used, coupled with an inversion algorithm and a forward model of fluid injection into a reservoir, to quantify the intake profile of treatment fluid along the wellbore. Recent field cases of matrix acidizing treatments in carbonate reservoirs are analyzed to illustrate the workflow and how it may yield valuable information. from Universidad de los Andes, Colombia.Kaveh Yekta-Ganjeh, P. Eng., SPE, is a senior technical engineer in coiled-tubing services at Schlumberger in Calgary. He has 10 years of experience in oilfield industry, all in coiled-tubing services. Yekta-Ganjeh joined Schlumberger in 2001 and has held different positions in field operation and technical support. He has worked in Iran, UAE, Libya, and Canada in land and offshore operations. Yekta-Ganjeh holds a BS degree in mechanical engineering from Sharif University of Technology, Iran.
Summary In this paper, we present a field example where pressure and distributed-temperature measurements enabled understanding of reservoir characteristics and fluid movement causing production hindrance in an offshore horizontal well. The field example has a horizontal well in the South China Sea that was completed as an openhole monobore oil producer using a slotted liner. The well began production with an initial oil rate of 1,800 B/D. Oil production quickly dropped to 1,000 B/D and gradually declined to 200 B/D. During this period, the gas/oil ratio (GOR) steadily increased from 200 scf/bbl to 2,200 scf/bbl. To arrest production decline, a chemical treatment was conducted to remove suspected emulsions and polymers assumed to have been deposited during drilling. Immediate post-treatment production increased to 3,700 B/D, but dropped dramatically and stabilized at pretreatment rates soon after. Formation of emulsions and asphaltenes were believed to be the cause of the production decline. However, with inadequate information, the diagnosis was inconclusive. Consequently, another chemical treatment was conducted and this time, a fiber-optic-enabled coiled-tubing (CT) string along with real-time bottomhole-pressure and temperature gauges were used to acquire distributed temperatures and pressures of the entire horizontal section of the wellbore. Results of the pressure survey revealed that the well was receiving insufficient pressure support from the water injector, which was causing gas-cap expansion. The distributed-temperature survey indicated excessive gas production from the toe of the horizontal section as a result of this expansion, thus limiting liquid production. The combination of gas rates with oil and water production has also created tight emulsions, further hindering production performance. It was concluded that the high gas production from the toe could not be selectively shutoff or controlled in the horizontal openhole slotted-liner completion to perform an effective stimulation program and treat the tight viscous emulsions.
fax 01-972-952-9435. AbstractThe concept of tracking coiled tubing (CT) failure statistics for use in developing performance indicators is not new. It has been covered extensively as the subject of previous abstracts. Tracking relies on an established process for reporting and investigation of pipe-related failures allowing the collection of data from CT operations of a leading service provider, which has global representation.The primary aim of the process is the identification of the immediate cause of the failure and, more importantly, the failure mechanism for the incident. Only with a good understanding of prevailing trends, if any, can remedial action addressing the root cause(s) of the problem be enacted. This is particularly important for an organization with more than 200 CT units and more than 750 CT strings in service over a wide geographic landscape. In an environment of high CT activity, which has been the experience of the last two years, the value of this process cannot be overstated.The value to overall CT operations is demonstrated in two examples in which the identified failure trends became the focus of separate service delivery improvement initiatives. The first issue resulted in a change in the organization's policy for reel storage and maintenance, while the second caused a modification in the CT unit controls to properly address the root cause. An in-depth discussion of the issues and their mitigation is the subject of this paper.The most recent paper on this subject presented information covering the period 1995 to 2000. This paper provides updated information on these CT performance indicators, presenting material from activities during the five-year period 2001 to 2005. The evolution of pipe failure trends is covered and contrasted against the changes that have taken place in the CT industry as a whole over the last decade.
Most coiled tubing (CT) string failures in the field can be traced back to some initial defects, such as mechanical damage, a corrosion pit, a manufacturing defect, etc. Because of the ductility of CT, the introduction of these initial defects doesn’t normally cause failure at the onset. However, over the course of the service life, these initial defects evolve or grow until they reach a critical stage, leading to eventual failure. To assess the serviceability of a CT string, the industry has largely relied on periodic pipe inspection using magnetic flux leakage (MFL). Since MFL signals arise from a complex combination of defect geometry, defect severity, and material anomaly, etc. in the pipe wall, they are very difficult to interpret. A "snapshot" inspection of the string may not provide adequate information to fully evaluate its integrity and/or future serviceability. To improve assessment of CT string serviceability, a new approach has been developed. The "continuous" inspection approach involves MFL monitoring of the CT string during utilization. With the continuous MFL monitoring from "new" pipe state through its entire service life, the MFL signal directly attributed to defects can be isolated and tracked, leading to an improved evaluation of the CT string’s condition and future serviceability. In conjunction with the theoretical fatigue life tracking, a new pipe Degradation Parameter is used to improve the management of aging coiled tubing. The state-of-the-art portable measurement and defect detection technology for CT strings uses MFL to detect the existence of defects and to measure wall thickness. It uses eddy current technology to measure the outside diameter (OD) of the pipe. MFL measurements are used to evaluate the defects over successive operations. Wall thickness and OD measurements are used in a real-time software to update the CT working envelope and the fatigue life. By integrating these features into a small portable device suitable for real-time inspection, this technology significantly improves the ability to monitor overall pipe integrity.
Distributed temperature sensing (DTS) is a fiber-optic technology that provides continuous temperature profiles along the length of a well. When placing the fiber inside a coiled tubing (CT), one can monitor the temperature evolution while pumping, as well as during a shut-in period. This evolution, in turn, yields some indications about the fluid placement performance or zonal coverage. So far, interpretation of such DTS traces has mostly been qualitative. The work presented here demonstrates how DTS data can be used, coupled with an inversion algorithm and a forward model of fluid injection into a reservoir, to quantify the intake profile of treatment fluid along the wellbore. Recent field cases of matrix acidizing treatments in carbonate reservoirs are analyzed to illustrate the workflow and how it may yield valuable information.
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