Degree

Doctor of Philosophy (PhD)

Department

Craft & Hawkins Department of Petroleum Engineering

Document Type

Dissertation

Abstract

Drilling fluid lost circulation leads to non-productive time and increases the overall well cost. In general, wellbore strengthening and lost circulation control are achieved by creating effective sealing structures to inhibit fluid flow through loss conduits such as formation fractures. This research aims at better understanding the effects of sealing structures in fluid loss prevention and remediation, and providing useful references to effectively establishing filtercakes on the wellbore and plugs in the fracture.

Recent research on wellbore strengthening disclosed the critical role of filtercake in sealing microfractures during the initial stages of fracture initiation and propagation. The performance of a filtercake to strengthen the wellbore depends on its capability to maintain integrity. In this research, a new parameter –“filtercake rupture resistance” and a new testing method are proposed to simplify the evaluation of the filtercake’s potential to withstand pressure over a small fracture. Experiments were conducted to understand the effects of fluid and filtercake properties on filtercake’s rupture resistance and on the effectiveness of filtercake in reducing fracture sealing time. The effects of filtercake with lost circulation materials (LCMs) in reinforcing fracture sealing were explored and it is recommended to consider the role of filtercake when evaluating the LCMs and designing lost circulation preventive treatment.

In addition to studying filtercakes for lost circulation prevention, this research also investigated LCM fracture plugs for fluid loss remediation. When drilling through naturally fractured reservoirs, the remediation of drill-in fluid loss needs to be designed considering both fracture plugging and formation damage. Statistical methods were used to better design the experiments and optimize the LCM implementation schemes, in order to efficiently create the desired fracture plug with less fluid invasion into fractures. The plug structure was visualized by SEM and Micro-CT scan to understand the effects of plug soaking process. A mechanistic model to calculate plug permeability with soaking time was developed for optimizing hesitation schemes.

This research presents new understandings about lost circulation and wellbore strengthening, and provides improved recommendations for optimal fluid loss solutions.

Committee Chair

Chen, Yuanhang

DOI

10.31390/gradschool_dissertations.5481

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