To reach drilling objectives in dynamic formations requires robust technology that can adapt to unpredictable wellbore conditions. Such is the case with operations in Asia Pacific; a very tectonically active region. The shifting plates put the earth's crust under extreme stress, which has a propensity to cause various difficult drilling conditions including:
High pore pressure
These issues are difficult to predict, both in occurrence and true vertical depth (TVD), and are usually mitigated by running an unplanned string of casing. Unexpected conditions requiring a casing point put the drilling plan at risk when reservoir objectives are hole-size dependent. Standard oil country tubular goods (OCTG) reduce the wellbore inside diameter (ID) every time a casing string is set. When the situation dictates setting casing higher than planned, solid expandable technology has successfully minimized wellbore reduction and enabled the operator to get back to the casing program with an optimized hole size.
Planning solid expandable systems into wellbore construction as a design element, rather than a contingency plan, has averted numerous problems identified during the drilling process.
Conventional solid expandable systems minimize loss of hole size, while single-diameter expandable systems (including openhole cladding) provide solutions without loss of hole size. By utilizing single-diameter technology, zones and formations can be sealed, allowing the next hole section to be drilled with the same bit as the previous. In this capacity, expandable systems become an enabling technology for previously undrillable wells.
This paper will discuss how solid expandable tubular systems have evolved to include a technology suite of options that addresses drilling challenges in active formations. Case histories will be used to illustrate the technical and economic value brought to projects by way of solid expandable system application.
The Asia Pacific region contains significant hydrocarbon potential in environments ranging from prolific, shallow-depth reservoirs to heavily-faulted, folded formations. Continental shelf margins as well as deep and ultra-deep marine environments have been explored and developed in this geologically-diverse area. Land and offshore basins yield production formations found in deltaic, fluvial environments, and stacked pay sections. This hydrocarbon-rich region is replete with ongoing tectonic movement, earthquakes, underwater landslides, lost circulation zones, and uncontrolled mud flows, as well as geologically stable and simple depositional environments. The prevalent conglomerate, igneous, clastic, and carbonate-laden formations present a variety of drilling challenges to regional operations.
Dynamic conditions add an extra element of difficulty when addressing the usual drilling problems such as lost circulation from a weak formation or borehole instabilities caused by complex lithologies. In an effort to preempt some of these problems, operators have taken to utilizing solid expandable tubulars by incorporating them into the initial wellbore design in both drilling and workover projects. Focusing on opportunity for the application of solid expandable technologies rather than on a need-based strategy has helped mitigate challenges once considered the hard boundaries that defined drilling limits and completion restrictions. The effectiveness of solid expandable tubulars to mitigate challenges has been well documented with over 920 applications to date. 1, 2, 3, 4, 5 Since the first installation in late 1999, the technology has evolved to include a suite of systems capable of addressing varied challenges even in extreme environments and dynamic formations.