Use of a Rotary Steerable Tool at the Valhall Field, Norway

Abstract

The overburden at Valhall consists of weak and partly fractured shale contributing to wellbore stability problems while drilling. To reduce the stability problems it is desirable to maintain a constant pressure on the formation, but this is not possible when drilling and tripping in a well. However, it is still important to minimize the pressure variation. An important factor here is to reduce the Equivalent Circulating Density (ECD) fluctuations when circulating the drilling fluid. Rotary steerable systems have been used on Valhall to improve hole cleaning and also to improve wellbore stability by keeping the ECD as low as possible while drilling. This paper forms a case history of several rotary steerable tool runs on the Valhall field, offshore Norway. The paper will, as an introduction, briefly discuss the different steering principles of available rotary steerable systems. In most fields the focus has been on using rotary steerable tools in the reservoir section; however, on Valhall they have been used in the overburden section. The reason for concentrating on the overburden at Valhall is because of the weak and fractured shale with it's wellbore stability problems. The paper will concentrate on the particular rotary steerable system used on Valhall, the Automated Guidance System or AGS Tool, which has been used to drill 12–1/4" × 13–3/4" holes. To be able to drill this hole size below a 13–3/8" casing string, a 12–1/4" bit was used below the Tool and a standard under reamer was initially used above. However in the two most recent wells, a specially designed near bit reamer, was used to drill the oversized hole. The automated guidance system has been used on 5 wells in the Valhall field and has made a total of 8 runs. Although none of these runs achieved the casing point, two of the runs set world records at the time, of more than 2000 m, and were regarded as major successes. Several runs were also planned at the limit of the Tool's specification. These runs were regarded as a combination of commercial and tool development runs, and were as such also considered successful. Comparisons will be made between the results from the different runs and the planned wellpaths. Also the actual automated guidance system wellpaths and similar mud motor runs will be compared in order to demonstrate the enhanced directional performance of the AGS Tool. Introduction The Valhall field is an initially over pressured, under saturated Upper Cretaceous chalk reservoir located in the central graben in the Norwegian sector of the North Sea. The reservoir is at a depth of approximately 2400 m subsea and consists of two oil bearing formations: the Tor and Hod. The former contains roughly two-thirds of the oil and is a soft chalk characterized by high purity (95–98 % calcite), high porosity (up to 50 %) and high oil saturation (90 % and greater). Oil and gas production from the Valhall field began in October 1982. The original 24 slot platform was first expanded to 30 slots in 1990, and then in 1996 a new 19-slot wellhead platform was installed. Plans exist to install a second wellhead platform in order to waterflood the field. The field was originally developed for recovery of 250 MM BO, but has already produced more than 450 MM BO and work is ongoing to prove and recover 1 Billion BO from the Valhall structure.

Investigation on the Technical Characteristics and Test Cases of RSS for Directional Drilling

“…방향이 일치하지 않기 때문에 시추공의 크기가 설계한 것보다 커지기도 하며, 시추공벽이 매끈하게 절단되지 않기 때문에 케이싱을 수행하기 전 시추공벽을 다듬기 위한 이수순환에 많은 시간이 소요된다 (Kinn, 2000). 푸시 비트를 이용한 RSS는 Fig.…”