A Unique Cost-Effective Technique for One-Trip Selective Gravel Packing Over Multiple Zones: Dacion Field Case Study
- John Marshall (Schlumberger) | Chike Obianwu (Schlumberger) | Raymond Tibbles (Schlumberger) | William Vargas (Schlumberger)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- December 2001
- Document Type
- Journal Paper
- 261 - 267
- 2001. Society of Petroleum Engineers
- 3.1.6 Gas Lift, 5.8.5 Oil Sand, Oil Shale, Bitumen, 3.3 Well & Reservoir Surveillance and Monitoring, 1.8 Formation Damage, 1.6 Drilling Operations, 5.1.1 Exploration, Development, Structural Geology, 4.3.3 Aspaltenes, 5.5 Reservoir Simulation, 3 Production and Well Operations, 4.1.2 Separation and Treating, 2.2.2 Perforating, 5.1.2 Faults and Fracture Characterisation, 3.3.1 Production Logging, 1.6.9 Coring, Fishing, 4.3.4 Scale, 2.4.3 Sand/Solids Control, 2.7.1 Completion Fluids, 2.2.3 Fluid Loss Control, 2.4.5 Gravel pack design & evaluation, 4.1.5 Processing Equipment, 5.1.3 Sedimentology, 1.14 Casing and Cementing, 5.1 Reservoir Characterisation
- 1 in the last 30 days
- 298 since 2007
- Show more detail
- View rights & permissions
|SPE Member Price:||USD 5.00|
|SPE Non-Member Price:||USD 35.00|
Selective gravel-pack completions of multiple zones present the oil industry with major challenges and expenses. Current practices have two key problems associated with them: they are limited to zones separated by 30 to 50 ft (depending on the treatment type) because of the length of the assemblies, and they have proven to have a higher risk of installation failure.
This paper describes equipment and procedures for gravel packing multiple zones in a single completion with total zonal isolation for spacing as small as 5 ft. Zones can be produced separately or comingled. Risk of execution failure is significantly lower than with conventional stacked packs. Production data is presented that verifies complete zonal isolation, improved productivity, and reduced costs from this technique.
The original Lasmo Venezuela BV development plan for the Dacion field called for single-zone gravel-packed completions and stack-packed multiple zones where intrazone space permitted. Early in the workover phase, before drilling commenced, it was realized that many of the oil sands would be covered up in a conventional gravel pack by the blank pipe, gravel-pack extension, and sealbore packer. With 60 ft of blank, extension, and packer, the normal spacing between gravel packs would be 85 ft. A lower net present value (NPV) would result in having to work over the original gravel pack at a later date to develop these reserves behind it.
Lasmo's first planned stack pack had only 21 ft between productive oil sands. The lower gravel-pack assembly was shortened to accommodate the required spacing. A high-rate water pack (HRWP) was achieved in the lower zone, but the crossover tool became stuck from gravel or because squeeze perforations above the gravel-pack packer had broken down during the pumping operations. This resulted in abandoning the lower zone after fishing attempts to retrieve the crossover tool from the packer bore failed.
Because of this stack-pack failure, the Lasmo/Schlumberger Alliance began to look for alternative solutions for completions in closely spaced multizone gravel packs.
The multizone system described here uses shunt tubes and specially designed isolation packers and requires only 5 ft of separation between perforated zones for complete gravel-packed zonal isolation. To date, more than 26 wells with up to 3 zones per well have been successfully completed in this manner.
Dacion and the Eastern Venezuelan Basin
A cross-sectional profile (Fig. 1) illustrates the complexity of the multiple sands found in the Dacion field.
The Dacion field in eastern Venezuela is a Miocene Age deltaic sequence of thin, highly permeable sands interbedded with shale and coal seams. The field consists of more than 530 reservoirs across 30 primary oil sands. To make recovery more difficult, the comingling of sands is not permitted, and most reservoirs have water drive. Typical sands are 20 ft high and may contain an oil/water contact. Some of the most prolific pay zones are separated by only 5 to 10 ft of shale. All zones require sand control.
The eastern Venezuelan basin covers 30 000 km2, containing an estimated 49 billion barrels of oil in place and having produced in excess of 6 billion barrels during the last 50 years from approximately 150 fields. Present production is approximately 250,000 barrels of oil per day (BOPD). The eastern Venezuelan basin is a classic Tertiary foreland basin.1,2 The principal reservoir in the Greater Oficina area is the Lower to Middle Miocene Oficina formation, which consists of interbedded sands, silts, and claystones with occasional lignites. At the time of deposition of the Oficina formation, the eastern Venezuela basin was a large embayment protected from the Atlantic Ocean by the uplifting eastern Serania. Core studies and regional geological correlations demonstrate the interplay of both fluvial and marine processes suggestive of deltaic deposition, with the paleo-water depth increasing to the northeast.
Petrographically, sands are clean quartz arenites consistent with a sediment source from the Proterozoic Guyana Shield to the south. Overlying the Oficina formation is the shale of the Freites formation, which makes a regional seal. However, accumulations within the Oficina formation are generally sealed effectively by intraformational seals, enabling multiple pay zones to occur in fields.
The basin is underlain to the north by a regionally deposited, late Cretaceous, anoxic marine, shelf-source rock within the Querecual and San Antonio formations that is believed to be responsible for the generation of all the oil found in the basin.3
The Dacion field is fairly typical of fields within the Greater Oficina area, with a large down to the south of the normal fault, offsetting reservoir sands against shales to form a stack of isolated petroleum accumulations with varying oil/water contacts. Sedimentological models for the Dacion field are still under construction but, broadly speaking, there appear to be two significant reservoir types—sheet-like bodies that typically show coarsening in upward gamma ray or self-potential log patterns, referred to as delta distributary mouthbars and linear sand bodies, typically with sharp bases and fining upward tops known as delta distributary channels.
Sheet sands and shoestring sands have long been recognized within the Oficina formation.4 An example of a correlation panel within the east Dacion area is shown in Fig. 1. Sheet sands have a variety of reservoir properties; the thicker, better developed bodies have very good reservoir properties and excellent cumulative production per completion. The thinner, more heterolithic sands have much poorer reservoir properties and have frequently suffered from extensive bioturbation, mixing silt and clay into the sands. Channel sands are more homogeneous by comparison and form the best quality reservoirs in the area.
Single-Trip Multizone History.
Multiple zones have been gravel packed in the past with a concentric workstring to manipulate fluid flow. This technique was developed offshore California for the Beta Project.5 A multiple zone assembly with isolation packers and a conventional upper gravel-pack assembly is used for the process. A concentric crossover tool, collets to indicate relative positions, shifting tools, and sliding sleeves for gravel placement are all run in one trip. This technique is unique for long zones in which rig time is at a premium and is not usually suited for land work. Because of the considerable cost of this type of assembly and a higher mechanical failure factor in the packing operation, it was discarded as an option.
|File Size||1 MB||Number of Pages||7|