Abstract

Many of the Deepwater Gulf of Mexico (GoM) development fields are maturing, making the challenge of drilling through these highly depleted reservoirs with narrow drilling margin a common occurrence. Some of these challenges include – 1) impairment of drilling operations due to mud losses while drilling & 2) inadequate cement coverage across stacked depleted reservoirs, which often requires remediation work. Proactive implementation of wellbore strengthening (WBS) techniques with application of Lost Circulation Material (LCM) is an established experience-based industry wide operation proven to help mitigate these issues. This paper discusses the WBS workflow implemented in the GoM to help minimize wellbore related non-productive time (NPT) events, building on previous published work (Tjioe & Husain, 2019). A GoM database comprising of subsurface information and drilling events collected over the last two to three decades provides invaluable insight into understanding the available drilling margin across different reservoirs. We present documented cases where this methodology is successfully implemented to execute multiple wells that required drilling and cementing across different highly depleted sands. Utilizing the database, the stress response is characterized in different reservoirs, which aids in Lost Circulation Material (LCM) design. We share an example where we performed an open-hole hesitation squeeze to control losses across highly depleted sands (ΔP = 3750 – 4500 psi) and improve the probability to achieve required cement coverage. The paper will also highlight operational learnings like LCM concentration reduction, etc which aid in smoother execution. This data-driven multidisciplinary effort has become the recommended operational workflow for WBS for Shell operated GoM assets.

Introduction

Losses during drilling or the cement job result in significant NPT in the GoM. Identifying the weak zone and appropriately treating it can dramatically reduce the NPT exposure. Other cost implications due to lost circulation events include consequences like sidetracking the well or running additional casing strings. Wellbore Strengthening (WBS) is a technique that is widely used to address such issues. Near wellbore stresses can be altered by implementing different WBS techniques to avoid mud losses during drilling.

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