Automated Drilling Fluid Rheology Characterization with Downhole Pressure Sensor Data

Abstract

AbstractMeasuring rheological properties of drilling fluids for optimum maintenance and wellbore hydraulic management is one the most important tasks during any drilling operation. In current drilling practice, such measurement is carried out by a mud engineer at the rig site using test protocols and equipment that quantify the relationship between the fluid's shear stress and shear rate, as standardized by API. Usually, measurements are conducted at atmospheric pressure and standardized temperature. Therefore, these rheological properties are generally not representative of the actual downhole pressure and temperature conditions, particularly not when it comes to deeper and more complex wells.This paper presents a novel method to determine mud rheological parameters in real-time by using downhole sensor data. The well itself is used as the equivalent of a large pipe viscometer, with pressure measurements conducted along its length using sensors placed at strategic positions in the drillstring. Contrary to traditional methods, rheology determination is performed automatically at downhole pressure and temperature, without any human interaction and without the need for any rheology measurement equipment on surface. Frictional pressure loss is recorded at several flow rates, preferably while ramping up pump rates after making connections, and parameters associated with two- and three-parameter rheological models (e.g. the n, K and τo parameters of the Yield Power Law (YPL) also known as Herschel-Bulkley model, which most accurately describes the majority of drilling fluids) are derived. In addition, time-dependent fluid characteristics such as gel strength can also be quantified using this method. Pressure data from wired (intelligent) drillpipe during field trials with a 12.6 ppg synthetic based mud was used to clearly validate the applicability of the new method in the field. Comparison of surface and downhole rheological parameters yielded excellent agreement, showing that the method can be applied successfully in the field when downhole pressure measurement techniques are available.This novel approach represents a significant step in the direction of achieving full automation of drilling fluid property monitoring and maintenance with an elegant method that requires no human interaction, eliminating the need for surface measurement equipment, while representing more accurately the downhole pressure and temperature environment. Given the importance of accurate rheology characterization, particularly in the new era of active annular pressure management using managed pressure drilling (MPD) and dual gradient drilling (DGD) techniques that rely heavily on accurate hydraulics modeling, the benefits are self-evident.