Introducing an Intelligent System for in Time Detecting Hazardous Shallow Gas Flows

Abstract

An intrusion of unwanted formation fluids into wellbore in presence of drilling fluid is called a "Kick". Kick happens because either hydrodynamic pressure of drilling fluid (ECD) is not sufficient against the pressure of formation fluids or with a sufficient mud weight, drilling operation reaches to a Geopressure formation with pressure greater than the pressure exerted by the drilling fluid dynamically. Study of 172 blowout cases world-wide shows that 33% of them were shallow gases, and the consequence of more than half of these was damage to or total loss of drilling rig. In this paper, focus is on major indications of shallow gas kick, specially flow line variations, and how dynamic and motional parameters of fluid can be utilized to detect kick quickly. Anatomy of a shallow gas, include its generation and geology is explained in this paper. Positive kick indications also are analyzed. All types of gas intrusion into wellbore formulas are evaluated and 6 new first time flow regime formulas have been derived from original formulas like annular Reynolds number annular velocity in both normal and flow conditions. A conceptional Annular Acceleration parameter has been introduced for the first time in the history of drilling engineering. Finally in the last, author suggests a real time monitoring system like those used in mudlogging units and assembled from sensors and monitoring software package that is tied with diverter system and runs the diverter operation automatically. The system can distinguish shallow gas from several events that happen in circulation system like mud weight modification, pit to pit transfer, mud dumping etc.