Tech Transfer Track

Casing Drilling and Underbalanced/Managed Pressure Drilling

In a recent Oil and Gas Roundtable meeting in Houston, Mike Bahorich of Apache Corp. cited some of their experience combining casing drilling and underbalanced drilling.

Since mid-2000 or so, the company has been drilling the tough Fort Worth Basin of North Texas. Typically, there are multiple producing horizons, many of which have very low formation pressures. Lost circulation or extreme formation damage are critical challenges and casing drilling performed underbalanced can address both.

Bahorich cited Apache's experience in the Stratton field. Here, the target is several interbedded Frio sands with bottomhole pressures varying from 90 psi to 2,800 psi. Using conventional drilling techniques on the first 22 wells drilled, Apache's average inflow potential (IP) had flat-topped at about 228 Mcfg/d. Starting in 2003 the company combined the UBD technique with casing drilling on three new wells and achieved solid results. Drilling time was down and production results up, averaging 753 Mcfg/d in 10 wells drilled in 2004 with casing drilling underbalanced. Consumables costs—fuel, mud and cement—were down measurably. Factors contributing to time savings included not having to run drillpipe, reduced bottomhole assembly time, and reduced "flat" time since the rig was always drilling. There were fewer hole problems and the well was always under control. And since casing drilling supports logging while drilling (LWD), real time data were available.

Apache's success with casing drilling has been experienced by BP in Wyoming and by ConocoPhillips in South Texas with results documented in SPE papers. Although not broadly used yet, there is evidence the technology combination is here to stay.

Excerpted from Dick Ghiselin's column in Hart's E and P (www.eandpnet.com/ep/previous/
0804/0804well_construction.htm), August 2004. Readers are encouraged to read a complementary article on "Blending Technologies (Casing Drilling and Managed Pressure Drilling) Can Eliminate Casing Strings" appearing in Drilling Contractor (www.iadc.org/dcpi.
htm), September/October issue.

Meeting quarterly, the Drilling Engineering Association (DEA,

www.dea.main.com) continues to be an effective vehicle for stimulating drilling technology advances. PTTC hosted the most recent quarterly meeting in Houston where updates were provided on active projects, new proposals were outlined and special presentations heard.

Active Projects:

• “Proposal to Develop an Improved Methodology for Pre-drill Pore Pressure and Fracture Gradient Prediction for Deepwater Wells (DEA-119)”—Jim Bridges, Knowledge Systems

• “Hard Rock Drilling Performance Improvement Through Impregnated Drill Bit Technology (DEA-148)”—Arnis Judzis, TerraTek

• “Modernization of Connection Performance Properties (DEA-151)”— Brian Schwind, PPI Technology

New proposals included:

• "Step Change in Directional Drilling Control and Efficiency when using Motor Steerable Systems (DEA-157)" —Slider LLP with sponsor, ChevronTexaco

• "Smart Shuttle (DEA-156)"—Smart Drilling & Completions & Triangle Technology A/S with sponsor ENI Norway

UWG Group, a consortium of companies, also described a separately launched JIP on "Pre Installation of Conductors."

Other special presentations included:

• "Long-term High Temperature Well Demonstration at Sandia National Laboratories" by Randy Norman, Sandia National Lab (www.sandia.
  gov/geothermal/htwell/)

• "Deep Trek Update" by Gary Covatch, DOE's National Energy Technology Laboratory.

Readers are encouraged to check the International Association of Drilling Contractor's website for the September/ October issue of Drilling Contractor (www.iadc.
org/dcpi.htm) for an article summarizing technical presentations made at DEA's June workshop in Galveston.

Apache Canada Ltd. (Apache) is applying top-down acid gas injection as an enhanced oil recovery (EOR) process to pinnacle reef reservoirs in its Zama Field in northwest Alberta. Secondary production there leaves about 65% of the oil in the ground. Sour production requires stripping. In conventional operations about two-thirds of the acid gas (two-thirds CO₂ and one-third H₂S) is disposed of through re-injection and the rest is processed into elemental sulphur. Processing releases CO₂ and there has been a persistent oversupply of elemental sulphur. Apache looked for other options.

Apache will inject acid gas into the top of pinnacle reefs. Acting as a solvent, the acid gas will drive oil down to a recovery well at the bottom of the pinnacle. In addition to recovering oil, the pinnacle reefs might provide long-term storage for CO₂ and H₂S sequestration. If all goes according to plans, sulphur-extraction operations at the Zama plant will cease, solving the sulphur stockpile program. Since operations were already handling the CO₂ and H₂S, additional handling risks are not created.

Initially two pinnacle reefs will undergo top-down acid gas injection, and there are plans to add one or two per year should things go as planned. Seven candidate pinnacles have already been identified within four miles of the Zama gas plant. Primary reservoir risk is controlling the injection/ displacement process to minimize channeling or fingering. Permeability can be quite variable in pinnacle reefs. Initial pinnacle projects will provide insight on achievable injection/displacement rates.

Excerpted from "Sweet Sour Gas Solution," New Technology Magazine, July/August 2004, pp. 22–23 (www.ntm.nickles.com). Apache contact for more information: Bill Jackson, Ph 403-261-1200, email bill.jackson@apache
corp.com.

Ever Wonder What All Those GIS Terms Meant?

DLG - ECW - DRG
SHP - TWF - DOQQ

View a slide discussion of GIS-related terminology, courtesy of Amigos Energy Advisors, LLC (www.amigosenergy.com/gisal
phasoup.pdf).