Managed-Pressure Drilling (MPD) Field Trials Demonstrate Technology Value

Abstract

Abstract Is this the beginning of the end of weighted mud systems? An advanced well control practice called Managed Pressure Drilling (MPD) is staged to challenge the conventional drilling practice of when in doubt "weight it up". Formation overpressures have traditionally forced operators to weight-up mud systems in order to advance drilling operations while preventing formation fluids invasion. A direct consequence of increased mud weight is a dramatic reduction in drilling Rate of Penetration (ROP), requirement for additional casing seats/strings and increased well control risks due to kicks from losses. This drilling hazard has represented a major source of invisible or intangible lost time and hence, cost. A drilling hazard mitigation multi-well trial was carried out to investigate and quantify the reduction in ROP as a result of mud weight increases to overcome troublesome formation overpressures and associated High Pressure Low Volume (HPLV) nuisance gas. Without increasing mud weight to control overpressures, MPD technology was applied to safely and cost effectively drill through overpressures and avoid an intermediate casing string normally used to isolate a loss zone. MPD trial results examined in this paper addresses many of the issues and provides forward-looking statements regarding large-scale introduction of the system to other fields. The multi-well trial results showed a close match to the predicted MPD ROP curve, achieving an economically rewarding ROP gain of at least 2.5 times and gross well cost reductions of over 20%, without recordable troublesome zone Non-Productive Time (NPT). Initial concerns of borehole instabilities using lightweight mud with borehole pressures less than the adjacent pore pressure were not observed (in both vertical and directional well cases). Introduction MPD technology is challenging the traditional drilling practice of weighting a mud system while drilling formation overpressures. MPD practices are suggesting that weighting up of a mud system is a major source of invisible NPT. Non-Productive Time (NPT) It has been reported by Dodson(1) that 25% of an average well's cost is recordable drilling NPT. As such, best practice Operators closely track drilling NPT. NPT is also commonly referred to as drilling flat curve time. Typical recordable NPT categories and key performance indicators used are as follows:Tight HoleDeviation ProblemsTool FailureHole Cleaning IssuesEquipment Failures and DelaysWell ControlLost Circulation Most Drilling Engineers have realized that Drilling Curves are under intense step change demands to reduce the time taken historically to reach a target depth. Tracking of NPT permits quantitative and statistical drilling analysis, to optimize drilling programs, control cost uncertainties (risks) and improve drilling economics. Drilling time is directionally proportional to cost, and in most cases, time saving (over cost) is the primary driver behind optimization strategies. Operators will often accept higher daily costs in order to save overall drilling time.