Over-pressured wells a risk for deepwater operations, says report

March 1, 2011
In a study designed to evaluate and address exploration and production (E&P) drilling risks associated with over-pressured formations, it was found that dramatically different magnitudes of overpressure existed across all 149 deepwater wells studied in the highly lucrative deepwater U.S. Gulf of Mexico Lower Tertiary Wilcox play. Understanding the variation and magnitude of overpressure is of critical importance, according to the authors of the study. They include officials from information and insight provider IHS and pressure consultants GeoPressure Technology Ltd. (GPT), an Ikon Science Co.

Bruce Beaubouef • Houston

In a study designed to evaluate and address exploration and production (E&P) drilling risks associated with over-pressured formations, it was found that dramatically different magnitudes of overpressure existed across all 149 deepwater wells studied in the highly lucrative deepwater U.S. Gulf of Mexico Lower Tertiary Wilcox play. Understanding the variation and magnitude of overpressure is of critical importance, according to the authors of the study. They include officials from information and insight provider IHS and pressure consultants GeoPressure Technology Ltd. (GPT), an Ikon Science Co.

TheIHS/GPT Deep-Water Gulf of Mexico Lower Tertiary Wilcox Pressure Study sought to gain an understanding of overpressure in the deepwater Gulf in terms of its distribution and potential impacts on future exploration of the region’s petroleum system. The study examined 149 deepwater Gulf wells, which were extracted from the IHS Pressure Database, a global dataset of re-interpreted, quality controlled, subsurface formation pressure data.

The study focuses on key wells in Alaminos Canyon, Keathley Canyon, Walker Ridge, Garden Banks, Green Canyon, and Atwater Valley, a combined study area that spans offshore acreage covering hundreds of miles across offshore Texas, Louisiana, and Mississippi in US federal waters. Water depths in the region range from 4,000 to 10,000 ft and depths of the wells can exceed 30,000 ft total vertical depth, subsea. Reservoir pressures in the Wilcox can exceed 20,000 psi.

The Lower Tertiary Wilcox trend covered in the study has proven to be a highly successful exploration target, with considerable upside potential of up to 15 Bbbl of recoverable oil reserves, according to IHS estimates.

“What we learned from the study is that overpressure variation has a significant impact throughout the play. Understanding the overpressure variation helps to minimize the drilling risk and inform on future exploration targets,” said Mark Diaz, senior geopressure analyst at IHS, and one of the study authors. “There are a number of operational challenges that exist alongside varying pressure regimes, including high bottom-hole temperatures, complex structural variances, and a canopy of salt that sits over much of the play, which makes the use of seismic data to visualize subsalt structures largely ineffective.”

“This study gives clients a set of analytical tools and supporting insight that enables them to make sound exploration decisions and minimize the potential risks associated with drilling when they have poor visualization of the subsurface,” said Sam Green, Ph.D., principal technical author of the study for GPT.

According to the report, all of the wells with formation pressure data that were studied indicated overpressure, although the degree of overpressure varied widely. The overpressures in the report ranged from 9.1 pounds-per-gallon equivalent mud weight (ppg EMW) up to 15.7 ppg EMW across the Miocene and Wilcox.

Analysis of the overpressure in the Wilcox showed that the highest overpressures are primarily in eastern Keathley Canyon and across the Walker Ridge protraction areas. The Wilcox data were analyzed with respect to compartmentalization versus lateral drainage as an explanation for the overpressure variation observed. The overpressure observations made in the Miocene have a significant impact on the subsalt play as a whole.

MWCC launches interim containment system

The Marine Well Containment Co. has announced the completion and availability of an initial well containment response system that will provide rapid containment response capabilities in the event of a potential future underwater well control incident in the deepwater GoM.

The initial response system includes a subsea capping stack with the ability to shut in oil flow or to flow the oil via flexible pipes and risers to surface vessels. The system also includes subsea dispersant injection equipment, manifolds and, through mutual aid among members, capture vessels to provide surface processing and storage. The company has consulted with the Bureau of Ocean Energy Management, Regulation, and Enforcement (BOEMRE) to ensure that the system is designed to meet the government’s requirements as outlined in NTL No. 2010-N10.

The MWCC interim system includes a subsea capping stack with the ability to shut-in oil flow or flow the oil to surface vessels. The system provides rapid containment capabilities in the event of a well control incident in the deepwater GoM.

ExxonMobil, in partnership with Chevron, ConocoPhillips, and Shell, continues to lead the development of additional system components to expand the initial system’s capabilities, with completion of the expanded system set for 2012.

“The Marine Well Containment Company has successfully developed a solution for rapid well containment response,” said Marty Massey, chief executive officer. “This milestone fulfills a commitment set forth by the four sponsor companies to deliver a rapid containment response capability within the first six months of launching the marine well containment project.”

The interim system can operate in water depths up to 8,000 ft and has storage and processing capacity for up to 60,000 b/d of liquids. The capping stack has a maximum operating pressure of 15,000 lb/psi. The equipment is located on the U.S. Gulf Coast.

Membership in the Marine Well Containment Co. is open to all companies operating in the US GoM. Members will have access to the initial well containment response system, as well as the expanded system upon completion of its construction. Non-members will also have access to the systems through a service agreement and fee.

OMSA calls for resumption of deepwater drilling

The Offshore Marine Service Association says it has launched a national campaign to demand President Obama stop destroying jobs, and allow deepwater oil drilling to resume in the Gulf of Mexico.The campaign kicked off with an open letter to President Obama, denouncing the suspension of deepwater drilling in the Gulf.

“President Obama has been trying to fool Americans into thinking that he lifted the moratorium on deepwater drilling in the Gulf,” said Todd Hornbeck, president and CEO of Hornbeck Offshore Operators and chairman of the Offshore Marine Service Association (OMSA). “Our education campaign will call him out on the facts: The Obama Administration is not issuing deepwater drilling permits, and the results have been devastating. It’s hurting tens of thousands of workers, increasing prices for gasoline and heating oil, and making America even more dependent on foreign oil.”

More can be found athttp://moratorium.offshoremarine.org/omsa/.

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