Ram/Powell Deepwater Tension-Leg Platform: Horizontal-Well Design and Operational Experience
- G. Scott Lester (Shell E&P Co.) | Gary H. Lanier (Shell E&P Co.) | Kaz Javanmardi (Shell E&P Co.) | Tony Bernardi (Shell Intl. E&P) | Afif S. Halal (Shell Intl. E&P)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- June 2001
- Document Type
- Journal Paper
- 117 - 126
- 2001. Society of Petroleum Engineers
- 2.2.3 Fluid Loss Control, 1.8 Formation Damage, 4.5.7 Controls and Umbilicals, 5.4.1 Waterflooding, 3.2.4 Acidising, 1.6.6 Directional Drilling, 4.5 Offshore Facilities and Subsea Systems, 1.7 Pressure Management, 2.7.1 Completion Fluids, 1.11.4 Solids Control, 4.2.4 Risers, 1.3.2 Subsea Wellheads, 3 Production and Well Operations, 2 Well Completion, 1.1 Well Planning, 2.4.3 Sand/Solids Control, 4.3.3 Aspaltenes, 4.5.5 Installation Equipment and Techniques, 5.8.5 Oil Sand, Oil Shale, Bitumen, 1.1.6 Hole Openers & Under-reamers, 1.12.1 Measurement While Drilling, 5.1.5 Geologic Modeling, 4.6 Natural Gas, 5.2 Reservoir Fluid Dynamics, 5.3.4 Integration of geomechanics in models, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 4.3.1 Hydrates, 1.10 Drilling Equipment, 1.11 Drilling Fluids and Materials, 4.1.5 Processing Equipment, 2.4.5 Gravel pack design & evaluation, 4.3.4 Scale, 2.2.2 Perforating, 1.3.1 Surface Wellheads, 1.14 Casing and Cementing, 4.2.3 Materials and Corrosion, 4.2 Pipelines, Flowlines and Risers, 1.6 Drilling Operations, 3.3.6 Integrated Modeling
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A key focus of the Ram/Powell project is to utilize high-rate (>20,000 BOPD), high-volume wells (i.e., reserves several times greater than that of shelf wells) to enhance project profitability. Completions with large 51/2-in. production tubing and horizontal openhole gravel packs (OHGP's) exceeding 2,000 ft in length have been implemented successfully. The horizontal OHGP design, the first implemented in the deepwater Gulf of Mexico (GOM), was selected as a means to improve well reliability over prior horizontal completion designs and sustain high production rates without plugging. A high rate of sand-control failure and plugging have plagued prior GOM horizontal non-gravel-packed completions. Achieving high-quality completions is a major project emphasis. Drilling, completion design, and operational experience of the horizontal wells are discussed.
Production from the Ram/Powell tension-leg-platform (TLP) development, Shell's third TLP, began in September 1997. The TLP is located at Viosca Knoll Block 956 in 3,214 ft of water. Four wells were predrilled prior to TLP installation. Ten wells are completed. Five are horizontal OHGP's, one is a single-zone cased gravel pack, and the remainder are two- and three-zone-selective cased gravel-packed completions. Rig operations concluded in January 2000.
Ram/Powell is a joint venture project consisting of three companies: Shell, BP, and Exxon/Mobil. Shell is the operator. The field is a unit consisting of eight leases in the Viosca Knoll area (Fig. 1). A TLP is set in a water depth of 3,214 ft in the 956 block. The platform is very similar to Shell's Mars TLP.1 The platform consists of five modules: production process and utilities, power generation, personnel quarters, drilling, and wellbay modules. The structure can accommodate up to 20 wells plus two well slots designated for top-tension oil and gas export risers. A removable platform drilling rig, capable of drilling to depths of over 20,000 ft, currently is installed. Waterflood facilities are installed for a possible future injection program; provisions are in place to accommodate potential subsea satellites. The initial nameplate capacity of 60,000 BOPD and 200 MMcf/D has been increased from a debottlenecking operation to 70,000 BOPD and 260 MMcf/D.
Much of the project design and fabrication tasks involved participation by technical and managerial staff from all three companies based in a single office. Joint company committees were formed to address key project issues such as selecting the development system.
In 1994 the project and subsurface teams revised the development plans to provide for some horizontal wells with larger tubing. This included increasing the dual-casing production-riser size from 95/8 in. to a larger 103/4-in. riser so that larger 41/2-in. production tubing with a full-bore surface-controlled subsurface safety valve (SCSSV) could be used. Subsequently, a maximum tubing size of 51/2 in. was incorporated to provide for even higher production rates.
Reservoir and Development Overview
Ram/Powell is a stratigraphically trapped sequence of turbiditic oil and gas reservoirs in 2,500 to 4,000 ft of water.2 The field was discovered in 1985. Three reservoirs are in the initial development phase: the J, L, and N sands, with expected reserves exceeding 200 million BOE. The J sand is a high-energy amalgamated-channel and sheet-sand complex. Two distinct rock types are found in the J: massive sands and laminated sands. There is a large oil rim with a large gas cap and well-defined gas/oil and oil/water contacts. The L sand is a channel/levee deposition consisting of numerous thin beds ranging in thickness with most beds less than 1 in. There is a small, uneconomic oil rim beneath a large, rich gas cap. The N sand is an amalgamated-channel oil sand with no identified gas or water contacts. The best quality reservoir sand is found in the massive sections of the J and N sands with core-plug permeabilities exceeding 1 darcy. Thin bed permeability in the J and L ranges from a few to several hundred millidarcies. Generally, these Miocene age sands are very well compacted, but have essentially no cementation bonding the sand grains together. Therefore, sand control is required in all well completions.
The sands are grouped closely between 12,500 and 13,500 ft subsea with original static pressure at 7,500 psi and static temperature near 220°F. The spider map in Fig. 2 depicts the proximity of the development wells with measured depths ranging from 15,805 to 22,155 ft. The crudes in the J and N sands are low in asphaltenes but were discovered to be highly paraffinic, with pour and cloud points significantly higher than GOM norms. All reservoirs are sweet, containing no H2S, but they do contain about 0.5 mol % CO2.
Development plans focus on draining the rich gas cap in the L sand with a near-horizontal, slant hole to maximize connectivity of the numerous thin beds. All J-sand wells are horizontal completions drilled at mid-elevation between the gas and water contacts to maximize recovery from the oil rim prior to draining the huge gas cap. N-sand development plans include a combination of conventional cased, perforated, and horizontal completions to drain this more complex reservoir.
Beginning in 1989, the joint company development committee considered numerous development scenarios, outlined in Table 1. The largest of these included as many as 75 well completions. Expected individual well production rates and recoveries were targeted at the current GOM high end of approximately 2,000 BOPD and 3 to 4 million BOE, respectively. Early scenarios planned for 31/2-in. tubing and 7-in. casing with conventional perforated, gravel-packed completions. By 1994, high-rate well studies, coupled with reservoir continuity and modeling studies, and development of horizontal drilling and completion technology, enabled new designs with the potential to yield an order-of-magnitude improvement in production rate and recovery per well completion.
Drilling Design and Experience
The drilling program includes batch-set and predrill operations conducted from a semisubmersible drilling rig prior to TLP installation and TLP-based drilling after installation.
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