Deepwater Batchset Operations Through the Magnolia Shallow Water Flow Sand

Abstract

ConocoPhillips is developing the Magnolia field with a Tension Leg Platform (TLP) in 4674 ft of water in Garden Banks (GB) block 783 in the Gulf of Mexico. Three wells were drilled at the eventual TLP site to discover and appraise the field prior to sanction of the development plan. Field development plans required drilling an additional six wells at the TLP site where a shallow water flow (SWF) zone is present. The development plan included batch drilling and casing the SWF interval prior to deepening any of the wells to total depth. The Magnolia batchset program was successfully conducted in 2002 using the Ensco 7500 dynamically positioned semi-submersible drilling vessel. The six well batchset program was drilled at less than the Authority For Expenditure (AFE) cost estimates with zero lost workday cases. The batch set program included jetting 36 in. casing to 246 ft below mudline (BML), directionally drilling a 26 in. hole to 3264 ft BML while building hole angles up to 17°, and running and cementing 20 in. casing with verified cement returns to the mudline. The SWF sand interval was drilled and cased without "Top Setting" a cemented casing string above the SWF zone. Although individual exploratory wells have been drilled and cased without top setting casing previously, the Magnolia field is the first deepwater field with a SWF zone to be developed in this manner. Pre-planning for the SWF zone addressed directional drilling issues, water base mud (WBM) design, cement formulation and placement procedures, and logistic supply to the drilling rig. Each well required three 89 ft joints of 36 in. casing, 81 joints of 20 in. casing, 40,730 bbls of blended WBM, and 6,760 ft3 of cement. Five supply vessels were used to provide logistic support for the operation. This paper will focus on the extensive planning process and the operational aspects of performing a batchset drilling program through a SWF sand in a deepwater environment. Introduction The well construction strategy for the Magnolia development wells included drilling the wells from a mobile offshore drilling unit (MODU) to total depth (TD) prior to the installation of the TLP. The "pre-drilled" wells would then be completed using a smaller, lighter completion rig installed on the TLP. This reduced the cost of the TLP due to the lighter deck loads than those needed for a full sized drilling rig and accelerated the production from the pre-drilled wells. The detailed planning and procurement of equipment for the pre-drilling program began in early 2002, immediately after project sanction. Remaining well construction personnel that were not already in place were selected and began planning the pre-drilling program. The completion design and pore pressure model determined the casing plan that was incorporated into the overall well design. Installing the 36 in. structural and 20 in. conductor casing strings for the development wells in a batch set mode at the beginning of the pre-drilling program was selected for the following reasons.Isolating the SWF sand with 20 in. casing and cement for all the wells before deepening any of the wells to TD would greatly reduce the cost impact if a SWF occurred that compromised the TLP site.Quickly capture efficiencies of repetitive activities by the drilling crews from the batch setting of the 36 in. and 20 in. casing strings. Taking advantage of coming down the learning curve quickly leads to significant cost savings.1The risk of a SWF occurring would be reduced since the rig crew would better understand and carry out the proposed plan of all six wells in a one month period versus drilling through the SWF zone once every six to eight weeks.To allow "leap-frogging" the subsea BOP between subsea wellheads during the pre-drilling program thus saving the cost and time of a round trip of the marine drilling riser and subsea BOP for every well.

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