Abstract

Underbalanced drilling (UBD) is a method where equivalent circulating density (ECD) is kept less than the effective pore pressure of the zone being drilled by 100 psi or more. Drilling in an underbalanced state provides a unique opportunity to gather real-time virgin reservoir data that would never be observed again after typical damaging effects from conventional overbalanced drilling. This condition allows formation fluid to flow into the wellbore during the drilling process, helping prevent drilling mud and associated contaminants from penetrating the producing formation, which protects the producing zone and minimizes the potential for formation damage. Proper instrumentation and drilling procedures allow acquisition of data that is then interpreted and analyzed to extract information about the reservoir. UBD benefits include:

  • Increased rates of penetration by up to 50%

  • Increased value by producing hydrocarbons while drilling

  • Increased production rates mean quicker payouts

  • Reduced formation damage

  • Reduced lost circulation costs

  • Reduced potential risks of differentially stuck pipe

An operator in India was truly the first to implement UBD technology within depleted reservoir sections of identified wells in an offshore asset. Three wells were planned as a part of the project. Project objectives, feasibility studies to determine applicability of the UBD technology to the selected field, an operational summary, and results of UBD operations on the first well are discussed.

Objectives for implementing UBD technology within the identified field included helping prevent reservoir damage, thereby enhancing oil production and recoverable reserves from the wells, and helping improve drilling performance within the reservoir section by eliminating mud losses, hence increasing lateral length and reservoir contact.

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