Abstract

Quantifying near well-bore formation damage by drilling and completion fluids at dynamic and static conditions is very important for a field development drilling and completion concept selection. This paper presents an evaluation methodology that combines results from dynamic/static filtration tests, returned permeability tests, and SEM tests on real cores with actual exposure time to fluids during drilling and completion into a well performance model to establish an invasion profile along the open hole section to quantify the impact on the productivity of the well.

A systematic laboratory test was conducted to evaluate the tolerance of a gas reservoir to damage by various mud systems. One water based system (WBM), two invert emulsion systems (OBM), a pure oil mud, a pure oil, and a pure oil emulsion were tested on real gas reservoir cores.

The water-based mud gave high return permeability, suggesting that filter cake lift-off alone is sufficient for the well clean up. This was supported by the good productivity from two appraisal wells that used a WBM. Test results showed that the OBM is more damaging due to the wettability change. This hypothesis is further strengthened as pure oil and pure old mud both provided good return permeability. SEM tests on the damaged cores indicate no particle invasion. Modeling results indicate that the well can tolerate the invasion by self-lifting off the mud cake. The WBM was therefore selected.

It is demonstrated that the methodology empowers the quantitative evaluation of near wellbore formation damage. As an example, the Changbei gas wells drilled with WBM can be self-cleaned-up that is confirmed by better than expected well performance.

Introduction

The impact of drill-in fluid on reservoir has been evaluated by research and field engineers for several decades. Recent literatures have been focusing on quantifying the degree of the impact on production and the uncertainties associated with the damage parameters1. For horizontal wells and multi-lateral wells, open hole or completed with slotted/pre-drilled liners, the importance of formation damage has been addressed both theoretically, experimentally and the combination of the two1, 2. Experimental procedures and equipment to evaluate filtration properties of drilling fluid under dynamic and static conditions have been developed3, 4 and are commercially available. Tools to simulate the influence of foreign fluid invasion into the reservoir and its effect on well performance have been developed and commercially available. This enabled us to quantify the effect of various drill-in fluids' invasion properties on well productivities, therefore, provided important information in helping the evaluation and selection of drill-in fluid based on fluid properties and drilling performance data.

The objective of this paper is to describe a methodology that could serve the purpose of combining laboratory experiment data, drilling performance data, reservoir properties data obtained during or after drilling to predict well productivity taking into account the impact of formation damage caused by drill-in fluids.

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