An Integrated Approach Towards Well Control of a HPHT Well

Abstract

Abstract Rising demand for energy has pushed the oil & gas exploration andproduction operations to harsher environments. High pressure and hightemperature (HPHT) is one of such challenging areas. HPHT developments presentchallenges at every stage. HPHT wells are defined as well having pressure above10,000 psi and temperature above 300°F. However the threshold is now pushing20,000 psi at 450°F. Many techniques that are applied to normal pressured wellmust be reexamined before its application in HPHT well else might result inconsiderable financial loss. High pressure and high temperature impact mud properties in a dynamic way andcan have major effect on well control. This paper presents an integratedapproach on impact of high pressure and high temperature on mud rheology andthermo physical properties. It also discusses mechanism of thermaldisintegration of different types of mud i.e. bentonite mud, polymer mud andoil based mud, and measures to extend their temperature limits. This paper alsodiscusses various symptoms and remedial action to improve mud properties. Preventing and controlling influxes of reservoir fluid into the well calledkicks are always central to drilling safety, but in HPHT wells the dangers froma kick are amplified. The three issues of HPHT drilling safety are kickprevention, kick detection and well control. This paper gives an overview aboutdetection of kick in a HPHT well, measures to prevent kick and well controlmeasures in case of a kick. Introduction The drilling of HPHT wells pose special challenges compared to standardwells:–High pressures and temperatures impact mud properties in a dynamic way, andcan have effects on well control–Increase in mechanical and fluid friction with well depth.–The majority of mud treatment chemicals derived from natural products beginto degrade at temperatures between250 and 275°F.–The volume of a HTHP gas kick remains virtually unchanged as it rises in theannulus from 14,000 to 10,000 ft [4265 to 3050 m]. From 10,000 to 2000 ft [610m] its volume triples. But from 2000 ft to the surface, there is a hundred-foldexpansion.–Put simply, a gas influx of 10 barrels at 14,000 psi becomes 4000 barrelsunder atmospheric conditions.–As reservoir fluid rapidly expands, it forces mud out of the well unloadingreducing mud in the well, cutting hydrostatic pressure at the formation, allowing additional reservoir fluids to enter, and ultimately causing ablowout. Drilling Mud Composition Drilling mud is a mixture of many components with different properties. Thevarious components react differently to pressure (p) and temperature (T). Thegas solubility and mixture properties of more complex hydrocarbon influxes varysignificantly. The most common components are base oil, water and weightmaterials (solids). Other components are chemically active, mix or dissolveinto the primary components of the mud for certain time periods during specificoperations on the well.