Underbalanced Drilling with Casing Evolution in the South Texas Vicksburg
- Douglas G. Gordon (Shell E&P Co.) | Richard J. Billa (Shell E&P Co.) | Michael B. Weissman (Shell E&P Co.) | Fu J. Hou (Shell Intl. E&P Inc.)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- June 2005
- Document Type
- Journal Paper
- 86 - 93
- 2005. Society of Petroleum Engineers
- 1.5 Drill Bits, 2.4.3 Sand/Solids Control, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 4.2 Pipelines, Flowlines and Risers, 1.11.2 Drilling Fluid Selection and Formulation (Chemistry, Properties), 1.7.5 Well Control, 1.6.10 Running and Setting Casing, 1.1 Well Planning, 1.14 Casing and Cementing, 1.7.1 Underbalanced Drilling, 4.1.2 Separation and Treating, 1.6.1 Drilling Operation Management, 1.11 Drilling Fluids and Materials, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 1.7.2 Managed Pressure Drilling, 4.1.5 Processing Equipment, 3 Production and Well Operations, 1.10 Drilling Equipment, 1.6 Drilling Operations
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Underbalanced drilling with casing (UBDWC) is improving drilling performancedramatically in south Texas fields.This approach allows drilling ofdepleted and high-pressure sands intermingled within one hole section,resulting in significantly less-expensive well plans.Drilling costreductions of 30% have been realized.Smaller-reserves targets areviable—a key advantage in the mature south Texas Vicksburg play.
Shell has developed and operated gas fields in south Texas for the past 50years. These 10,000 to 16,000-ft, high-pressure/high-temperature wells normallyhave initial shut-in tubing pressures approaching 10,000 psi when virginpressure sands are completed.The bottomhole temperatures range from 280to 400oF.Most wells have multiple low- permeability pay sands, whichrequire massive hydraulic-fracture treatments to produceeconomically.Each pay interval is fracture treated in a separate stage,and the production from all the sands is commingled.
Most current drilling activity is in and around mature fields in which largevolumes of gas have been produced.Severe reservoir-pressure depletionintermingled with high pressure is often encountered.The presence andlevel of pressure depletion is difficult to predict because of complex geology,low permeability, and production commingling.
The UBDWC approach was first applied to a slimhole re-entry program thatbegan in 1995.These re-entries were either sidetracks to replace wellsthat failed because of casing damage or wells that were deepened to newobjectives.The re-entries are normally half the cost of a new well,allowing smaller reserve targets to be drilled economically.The wellswere sidetracked out of the existing 5- or 5½-in. casing and a new string of2?-in. casing was run and cemented.By 2000, the remaining re-entrycandidates were difficult to drill, with lost-circulation and well-controlproblems more common.The program was becoming uneconomical because of theinability to set liners in the small hole size.UBDWC1-3 was applied toresolve these problems, and 10 re-entries have been drilled this way since2001.The low-permeability Vicksburg sands allow operations with a higherunderbalance than would be possible in most other applications.
The learnings from the re-entry program have been transferred to thedrilling of new south Texas wells.This has allowed smaller casingprograms and the elimination of liners, and trouble cost has been reduced,resulting in a cost savings of up to 30%.UBDWC requires little rigmodification and standard off-the-shelf equipment; it has been applied on rigsequipped with rotary tables and top drives. Using the Intl. Assn. of DrillingContrators' Underbalanced Operations Classification System, these operationsare Level 5-B-5.
|File Size||539 KB||Number of Pages||8|
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