Lost circulation is commonly encountered in drilling and cementing operations and can be a costly challenge to overcome. During cementing, lost circulation can compromise zonal isolation and, ultimately, impede production. Risks associated with lost circulation affect most applications, particularly those in highly permeable and depleted formations. The manuscript describes a new tailored spacer system designed to effectively mitigate lost circulation and its application in cementing unconventional wells to meet zonal isolation objectives.

The tailored spacer system was employed in a Delaware Basin cementing operation to prevent lost circulation through a subterranean section historically prone to losses and subjected to well construction regulations. Laboratory testing prior to the job verified operational criteria would be met. The tailored spacer system was successfully applied, providing improvements to complete returns of wellbore fluids back to surface, and helped eliminate remediation needs.

Introduction: Delaware Basin Operations

Oil and gas operations in the Southeastern New Mexico area of the Delaware Basin are performed on United States Federal Government owned land. The Bureau of Land Management (BLM) administers these federal lands, and parameters affecting well construction and production are guided by regulations in place to protect the lands and resources therein. Well cement coverage requirements are in place for hydraulic fracturing operations to proceed, and remediation may be needed if casing is not cemented to surface. Despite these regulations, the southeastern New Mexico area has been attractive due to reportedly highly productive and profitable wells (Willis, 2018).

Lost Circulation Risks and Common Mitigation Approaches

Cement coverage considered inadequate may be signaled by a number of indications, including lost circulation, cement fall back, channeling of cement, and/or equipment and process failures during the operation. Notably, lost circulation, which may also be tied to cement fall back, is common to drilling and cementing practices in general, and particularly problematic in highly depleted sand formations of the Delaware Basin. The attractiveness of wells in this region have led to substantial development over the last decades, and, through this time, continual production has left fields depleted with declining pore pressures and associated fracture gradients. Ultimately, heightening risks of fluid losses impedes operations. Lost circulation may be categorized as seepage, moderate, severe, and/or total by their associated rates, i.e. volume per time unit (Nayberg, 1987; Nelson, 2006). Different mitigation approaches to prevent or responses to cure losses may be employed depending on the category of losses encountered. To mitigate risks of lost circulation, the well design strategy may exhibit features to isolate lost circulation zones (Willis, 2018). Furthermore, operational practices, e.g. managing equivalent circulating densities via pump rates, are implemented with the formation properties and limitations in consideration. Managed pressure drilling and cementing (MPD and MPC) techniques have been employed, as well, to reduce risks of poor returns when circulating across thief zones (Thibodeaux, 2018).

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