The timing of recruitment for age‐0 bluefish Pomatomus saltatrix along the southern and mid Atlantic coast of the USA is bimodal, consisting of spring‐spawned and summer‐spawned cohorts. We present evidence from surveys of age‐0 fish that the recent precipitous decline in the Atlantic bluefish stock over the past decade has been associated with a switch in the relative production of the two cohorts from predominance by spring‐spawned fish throughout the 1970s and 1980s to predominance by summer‐spawned fish in most years from 1992 to 2002. Given this evidence of a shifting recruitment pattern, we reexamined the contribution of the two cohorts to the adult portion of the population and compared our results with similar earlier assessments. Cohort origin of adults was identified based on back‐calculated length at age 1. In four year‐classes in which age‐0, summer‐spawned bluefish predominated, there was little evidence of summer‐spawned fish among harvested adults from the same year‐classes captured one or more years later. Most adults examined in this study (N = 976) displayed lengths at age 1 greater than 20 cm, as predicted for spring‐spawned bluefish. This contrasts with year‐classes of bluefish from the late 1950s, when back‐calculated size at age 1 was clearly bimodal, consisting of both spring‐spawned and summer‐spawned cohorts. Low numbers of summer‐spawned bluefish in our samples did not appear to be an artifact of inaccuracies in aging or back‐calculation. The recent decline in the abundance of Atlantic coast bluefish appears to result from poor age‐0 recruitment of the spring‐spawned cohort and failure of the summer‐spawned cohort to contribute substantially to the adult population.

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The successful development of a light weight slurry system for cementing long intervals at high temperatures in three dimensional multiple stacked gas zone wells, has been achieved in the Gulf of Thailand. The cementing system has been developed to successfully complete progressively more difficult wells, starting with conventional large bore wells and tubing plus packer completions, and later down-sizing into single monobore wells whereby the tubing is cemented in place. The problems associated with the down-sizing of the wells are further increased by more challenging well paths and higher temperature fields. Many problems and risks were overcome to complete this task successfully. These changes have posed new challenges in primary cementing. Like the well size, the slurry system has also undergone a refinement and improvement process. The local industry has gone from dry blended slurry systems to all-liquid additive slurry systems saving considerable dollars, whilst realizing large gains in slurry flexibility, ease of mixing and improved logistics. Whilst developing and realizing these gains, the system has been refined and successfully applied to smaller, hotter and more difficult wells. This paper presents the concerns associated with cementing these challenging wells where remedial cementing has been effectively eliminated. The processes related to this success, evaluation methods and field results will be discussed. Introduction In terms of completing the well, cementing operations are arguably one of the most important operations done on a well. When performed correctly they give a well every opportunity to perform as it was designed. However, poor primary cementing can lead to lost reserves, increased water rates and expensive remedial work. The prime goal of cement is to provide adequate zonal isolation throughout the life of the well. This is essential for trouble free production. In slim hole cementing the importance of adequate zonal isolation is magnified due to the fact that remedial options are both limited and also expensive. Unocal Thailand has drilled over 1400 wells (Figure 2) in the Gulf of Thailand. During this period there have been many changes in well design. This paper will deal with the two most recent. Older completions utilized 13 3/8" casing to 1,000', 9 5/8" casing to 4,500’ TVD (+/-7,000’ MD) and 7" casing to 8,900’ TVD (11,700’ MD) with a conventional packer and sliding sleeve completion installed for production. One recent change occurred with the elimination of the 13 3/8" casing and conventional completion. The resulting wells were completed with 9 5/8" casing, 7" casing and 2 7/8" tubing being cemented in a 6 1/8" hole. The 9 5/8" casing is set at 1,000 TVD, the 7" casing at 4,500’ TVD and the tubing is run to TD at 8,900’ TVD (Figure 1). To date 627 of these wells have been completed. The most recent change has been to down-size one more level with the elimination of the 9 5/8" casing. This has been achieved by setting 7 5/8" casing at 1,000'. The 7" intermediate casing from the original Gulf of Thailand Monobore well has become 5 1/2" casing. Finally the production hole is drilled with a 4 3/4" bit and the same 2 7/8" tubing cemented in place. This ultraslim well architecture has been used on 13 wells to date. The well paths of all types are predominantly three-dimensional with 35° to 60° inclinations and 90° azimuth changes. These wells are intersecting alternating sand shale formations with numerous thin coal seams. The sandstone reservoirs contain gas condensate and high CO2 with an average thickness of 13 feet. The reservoirs themselves are broken into many smaller sections as a result of being in a complex faulted graben system. In addition to this, there are multiple gas/water contacts in the wells, making isolation essential for trouble free production.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractWater production in mature fields is a common situation. In many mature areas, every barrel of oil is being produced with six to ten barrels of water. The production of water results in increased operating expenses along with other water related well problems like scale, fines migration, sand face failure, water loading in wellbores etc.