No abstract

The criteria for success of any primary cementing job is achieving permanent zonal isolation. Incomplete mud removal will affect the zonal isolation in several different ways and may lead to the development of a communication channel in the annulus and subsequently jeopardize the well integrity. Nonaqueous fluids (NAF) are incompatible with cement slurries; the quality of the cement placement and set properties will be strongly affected by the presence of the NAF residue down hole. Although this problem can be mitigated through the addition of various chemicals providing compatibility, mud-thinning, reduction of the interfacial tension, and water-wetting functions, the current surfactants and solvents on the market have limited application in terms of temperature and type of drilling fluids. In addition, the current API/ISO testing protocols are generic and results are not reproducible. Recently, improved laboratory procedures have been proposed and these improved experimental methods were used on more than 200 surfactants and solvents. A screening process helped in selecting the optimum chemistry as a function of the conditions (type of base oil, salinity, temperature). This enabled developing design guidelines to select an optimized tensioactive package comprising a limited number of chemicals, from which field users would select the ones to combine for their applications. The new tensioactive package was used successfully in two field trial wells in the 7-in. liner sections in a mature development field offshore Thailand. After a thorough comparison between the currently used package and the new one, the laboratory results using the field mud show superior cleaning results and efficiency with the new chemical package. The zonal isolation was confirmed using an ultrasonic imager logging tool. After the two successful field trials, the tensioactive package was selected as the spacer of choice for a critical new development field campaign offshore Thailand in which zonal isolation between production zones was critical for selective production from each of the zones separately. This paper will describe the newly improved laboratory methodology and selection criteria of the new tensioactive products and provide a detailed case history of the application in the development campaign, including the design, execution and evaluation of the job.

Summary Lost circulation is a time-consuming and expensive challenge, costing the oil and gas industry billions of dollars each year in materials, nonproductive time, and minimized production (Catalin et al. 2003; Fidan et al. 2004; API 65-22010). To mitigate lost circulation during cementing operations, a better understanding of how wellbore-strengthening mechanisms apply to cement slurries is necessary. The ability to control cementing-fluid properties to strengthen the wellbore and minimize losses during cementing operations is imperative for achieving adequate zonal isolation. A field analysis was performed to understand the start of lost circulation during different phases of drilling and primary cementing. Offshore wells from four different locations were studied: Gulf of Mexico (GOM), the UK, Angola, and Azerbaijan. In parallel, laboratory research was performed to understand the behavior of cement slurries in controlled lost-circulation scenarios using a block tester. Measurements of formation-breakdown pressure and fracture-propagation pressure were made with different cement-slurry compositions and compared with pressures obtained with drilling muds. In an analysis of 40 well sections that reported losses before or during primary cementing operations, the rate and severity of lost circulation varied for the wells studied, but it was concluded that losses were commonly induced while running casing or during precement-job mud circulation, but rarely during cement placement. The laboratory research confirmed the field observation: It would take much more pressure to open or reopen an existing fracture with cement slurry than with a synthetic-oil-based mud. This paper will present findings from the field analysis and laboratory research. It will also discuss strategies to prepare the wellbore for preventing losses before the cementing operation and to optimize cement formulations if losses have been induced during drilling, casing running, or prejob mud circulation.

No abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe numbers of ageing fields in North Sea are only increasing as more and more brown fields are reaching end of productive life. The challenge today in the North Sea is to maximize production from what remains and also to safely, economically and optimally abandon the wells, which can no more produce. The operators have hence started looking for options to abandon wells in a highly government regulated environment. Permanent Plug and abandonment is done with the objective for the well to be sealed and isolated forever. This long term sealing requirement is one of the principle parameters to measure the success of abandonment. This becomes even more critical in the North Sea as the cost of operating offshore and risked cost of returning to re-abandon a leaky well run into millions of dollars. Furthermore the environmental liability of cleaning up slicks from a leaky well is also a concern. Technically sound abandonment practices are necessary for long-term isolation to protect the environment and to avoid the eventuality of an expensive re-abandonment. This paper presents a) A discussion of abandonment regulations and requirements. b) A case history for permanent abandonment campaigns in the North Sea region UK sector. c) A discussion of the methodology, materials and techniques used.