Publications

The oil and gas industry continues to demand cost-effective and well-designed operations. Well design optimization reduces the total Authorization for Expenditures (AFE) by decreasing drilling time and cost. Well design is not a fixed pattern throughout the life cycle of a field; it should be continuously optimized through improvements in all aspects of well architecture, depending on actual field conditions and economic sensitivities. The core objective of this study is to provide an in-depth review of successful well design optimization based on field cost sensitivity and drilling performance.

Well design optimization processes include unconventional design, such as slim-hole architecture compared to conventional (fat) architecture, eliminating unnecessary casing design and trajectory, optimizing casing seat selection, and managing casing string loads. Eliminating unnecessary casing design and trajectory results in a long open hole which, by default, creates new challenges that must be addressed and solved without compromising the targeted cost saving. The challenges can be summarized as follows:

Combining loss of circulation zones with unstable shale formations in a single section

Managing PPFG uncertainties

Ensuring efficient hole cleaning and displacement when changing mud systems

Optimizing BHA selection and drive optimization.

Optimizing casing seat selection helps avoid serious problem such as kicks and losses, which increase nonproductive time (NPT) if kick tolerance and the downhole pressure profile are not considered. Anticipating optimal stress loads in casing design is the most effective way to reduce casing strings costs while avoiding unnecessary cost associated with designing for extreme worst-case scenarios.

The aforementioned optimizations significantly reduce drilling cost and time. Slim-hole architecture, achieved with smaller casing and hole sizes, lowers costs related to volume, tubular materials, and fuel consumption. Since the first implementation of this approach, the team has successfully achieved a 33% reduction in dry hole cost per foot, delivering wells and producing oil 25% faster. This paper not only describes how a two-string design was successfully engineered and executed but also serves as a guide for selecting proper candidates for this design. Additionally, it provides an operational guide for two-section well designs to ensure that these challenging long open holes are successfully drilled while minimizing risks.