Keeping complexity under control

Nicole Ramsey Braley, Weatherford, explains how a framework for real time geomechanics optimises drilling and borehole stability in complex reservoirs.

As operators drill increasingly complex wells in basins worldwide, they require real time solutions to mitigate nonproductive time (NPT) and address unforeseen drilling-related problems such as borehole instability, stuck pipe or lost tools. Drilling-related problems drive up costs by as much as hundreds of thousands of dollars per day. Wellbore instability also can lead to well-control events that result in additional costs for environmental cleanup, diminished safety records, regulatory fines, and damage to a company’s reputation.

Geomechanics is the application of solid mechanics, mathematics, and physics to quantify how rock fractures respond to various factors. (Source: Weatherford)

It becomes increasingly clear that overcoming drilling-related issues requires greater understanding of the reservoir subsurface. The oil and gas industry has recognised the importance of taking a proactive approach through geomechanics - the application of solid mechanics, mathematics and physics to quantify how rocks and fractures respond to factors such as excavation, changes in fluid pressure and temperature, redistribution of stresses, and physio-chemical phenomena.

Taking a framework approach

Comprehensive geomechanical characterisation has proven to be highly beneficial using a framework applied during the pre-drill, drilling, and completion phases of the well life cycle. The framework, which can be tailored to a specific well profile, integrates tools and technologies for analysing data to give operators a more complete picture of the reservoir and a view of what is happening downhole in real time. The framework gives operators needed insight to adjust drilling plans and trajectories and ultimately to achieve greater value and improve field economics. Weatherford developed the geomechanical framework for all well types, but the approach is proving especially beneficial in extended-reach unconventional wells, where wellbore stability issues can be significant.

Supplementing the MEM

The cornerstone of the framework approach is data. Initial mechanical earth models (MEMs), which rely on existing data, are supplemented with geophysical and image logs and with reservoir, geological and seismic data. Data from offset wells also provide valuable information about the reservoir and surrounding wells that can affect production.

For each offset well, data obtained from logs, drilling and hydraulic fracturing information, geological characteristics, surveys and well plans are calibrated and validated with drilling events, cavings analysis, core analysis data, formation pressures, and leak-off tests. The resulting 1D, 2D, or possibly 3D geomechanical model, with a focus on wellbore stability, is then used to determine the parameters of the proposed well, including correct mud window and mud weight, casing shoes, rock mechanical properties, risks and contingency analysis of borehole stability. Geological pressures, which can be affected by depletions, subsidence, weak planes and tectonic deformations in the region, must also be considered.

Real time updates

Because the MEM is continually supplemented and enriched with new data in real time during drilling, the framework enables operators to navigate the sweet spot while recirculating information and conducting performance benchmarking. Operators can quickly respond to conditions such as pressure increases or changes in stress distribution that require a shift from the initial drilling plan. The data, developed in conjunction with slickline and wireline logging, can be used to improve both drilling and cementing operations by helping operators to see how pressures are affecting the trajectory.

Geomechanical characterisation represents new thinking by an industry facing ever-increasing challenges. It also enhances the capabilities of tried-and-true methods that operators have relied on for years. The framework to improve pre-drill plans and enrich MEMs while drilling is giving producers the specific tools they need to optimise drilling and achieve wellbore integrity in complex reservoirs, while mitigating borehole stability issues that can result in NPT, increased cost and greater risk.

Adapted by David Bizley

Published on 29/01/2015

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