A Practical Approach to Evaluating Directional Drilling Performance

Abstract

Earlier attempts to establish DD performance using the directional drilling difficulty Index (DDI) proposed by Oag & Williams1 is flawed and difficult to interpret. The philosophy behind the DDI relationship is based on the perception of a sample space. Thereafter a mathematical relationship between the "perceived" variables identified within the sample space was proposed. DDI can only be applied for performance benchmarking if the planned DDI can be related to the actual DDI. DDI can only be used to compare the difficulty of drilling wells from the same terrain and to similar vertical depths. Since DDI does not consider adherence to the plan to account for differences between plan and actual drilled paths it therefore does not provide much information in the way of performance monitoring or benchmarking. Is there a need for directional drilling performance monitoring? Is it possible to isolate other methods of measuring performance such as finance or time based relationships? Are we able to demonstrate directional drilling performance in such a way it becomes possible to eliminate the impact of differences and variations in service prices, service tiers, competency of rig crew and rig capability, terrain, etc? This makes the cost based approach quite restrictive in its application in establishing a key performance indicator for directional drilling activities. Traditional methods2 for measuring performance use metrics such as cost/foot, cost/10000 metres or feet, NPT distribution, ratio of NPT-to-Exposure time for specific services, $/BOe and days on well to name but a few. Generally, the metrics are designed either as time or cost based relationships. The implication there of is that directional drilling competency or performance is somewhat lost within the generalized approach this method requires where information is normalized into time or cost based variations. Therefore, directional drilling impact on the drilling cycle becomes a measure of how quickly the well is drilled with little or no consideration on how to get there and the impact of the tortuous part drilled on the outcome and performance of the well. This paper does not suggest the elimination of traditional methods but looks at ways of establishing a performance metric between the values 0 and 1 that can be used to compare directional drilling performance whilst still capturing the essence of time and cost based relationships. Furthermore, this method becomes extremely easy to use and can be easily computed at the well site using a simple spread sheet solution as the inputs for each well can be obtained from the standard directional survey file and the daily drilling reports. The application of the results include benchmarking performance from well-to-well, across projects, contractors and fields and to understand the influence of directional driller competency and geology on the final performance indicator. Introduction Directional well surveys are defined by the following:Surface location usually expressed in terms of a geographical or UTM co-ordinatesA subsurface target which is also defined by specific co-ordinates which are usually not the same as the surface location unless in specific cases. This is also further defined in terms of a target tolerance around a specific vertical depth reference.The standoff between the surface location and the subsurface target(s) usually establishes the DLS (or BUR in case of a 2D well) requirement, the directional well path which includes inclination and azimuthal variations and the sail angle through the target(s).