Mud weight optimization is a critical driver to successfully drill horizontal wells. Historically, using inadequate mud weight while drilling horizontal wells has proven to be cost effective when it is intended to place multistage fractures in tight formations. The typical problems encountered in such wells are tight spots, requiring hard reaming which sometimes lead to stuck pipe and bottom-hole assembly (BHA) loss during borehole events. It is of paramount importance in drilling that correct mud weight be used from the start and during each section. Subsequently, based on well behavior/response, mud weight is optimized to an optimum range during the course of drilling.

In subsurface areas where rock behavior varies progressively with depth, along with constantly changing regional and local stress regimes, mud weight optimization is one of the tools that lead to successful drilling of wells to depth (TD). Geomechanical characterization of the target formations provides optimum mud weight window to drill along planned trajectory with minimum wellbore stability related issues.

This paper describes the construction of a 1D Geomechanical model and wellbore stability (WBS) analysis performed to determine the mud weight window used to drill multiple sections in a horizontal well for a new offshore field. The paper will further discuss how an integrated drilling and geomechanics approach was utilized for mud weight and drilling/tripping practices optimization, which resulted in successful drilling

This study is a perfect learning example how to use the various surface and downhole data in real-time and integrate it with a pre-drill geomechanical model to forecast and avoid wellbore stability/drilling problems by optimizing mud weight window. The value of geomechanical study is not only limited to drilling the well to TD, in fact, updated information can be further utilized for finalizing completion strategy. This paper also describes how updated stress profile in 1-D geomechanical model was used to characterize the reservoir for multi-stage fracturing.

A comprehensive geomechanics study incorporating offset wells analysis, core data, mini-frac data and formation pressure points resulted in the following starting mud weight recommendations for each section of the horizontal well in tight formation:

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