Technical Limit Specific Energy - An Index to Facilitate Drilling Performance Evaluation

Abstract

Abstract This paper describes a method developed to represent the inherent drilling difficulty posed by the combination of rock properties, depths and pressures that make up a field's drilling environment, thereby facilitating comparisons of drilling performance from different fields that take account of varying rock "drillability". The method uses the concept of specific energy - the lower the specific energy in a given environment, more efficient the drilling process. An algorithm has been developed to estimate the technical limit specific energy from wireline sonic, lithology and pressure data. This represents lowest specific energy that can reasonably be expected for that combination of rock properties and pressures. Data were analyzed from 10 wells, drilled in varying on and offshore locations, which were selected as good benchmarks the performance achievable in their drilling environments. Three measures were used to represent drilling performance in these wells - total dry hole (excluding coring, logging and completion activities) days per 1,000 m, normal drilling days 1,000 m, and rotating days per 1,000 m. These measures showed wide variations across the 10 wells, reflecting the range in drilling difficulty posed by the different geological environments. However, the rotating days per 1,000 m showed encouraging correlation when plotted against the wells. technical limit specific energies. The other performance measures also showed clear trends when plotted against technical limit specific energy. The existence of these correlations demonstrates that technical limit specific energy a valid measure of whole-well drillability, and provides a benchmark against which other wells' drilling performance be compared. The performance measures for the new well are compared with the "benchmark performance" trends at the new well.s technical limit specific energy, revealing whether the drilling performance departs substantially from the expectation for well of similar drilling difficulty. Introduction A major western operator recently entered into a joint venture with a Russian oil company. Historically the Russian oil company's wells have been drilled using indigenous equipment, techniques and management structures. As part of a comprehensive performance benchmarking effort, the new organization wished to investigate performance levels prevailing in the joint venture's drilling operations and compare them with those achieved in other regions where Western equipment and techniques are used. A service Company's drilling performance optimization group was engaged to assist with the investigation. It was recognized at the outset of the work that some method to represent and to make allowance for the difficulty of drilling inherent in each environment was necessary if valid performance comparisons were to be made between different regions. This paper describes the method that was developed to do this. Drilling Performance Measures Several different criteria for assessing drilling performance can be identified. Health, safety and environmental performance are crucial, however criteria for assessing them are outside the scope of this work. Next are the well's overall objectives in terms of reservoir access and data collection. If these objectives are clearly stated, it is straightforward determine whether or not they have been met. Once the objectives have been met, drilling performance is often assessed in terms of the time taken to construct the well, and the well's total cost. Plainly the distance to be drilled varies from well to well. Rig operating and service costs can and do vary from location to location. So the time taken to drill fixed depth interval is widely adopted1 as a measure of drilling performance and as a basis for drilling performance comparisons, assuming the well's objectives have been met.