Mitigating Risks From Waste Subsurface Pressure Injection and Decline Analysis

Abstract

fax 01-972-952-9435. AbstractThe progression of new field developments, including brownfield and deepwater, subsequently increases the volume of cuttings and production waste, and particularly produced water, considerably. The economical impact of missing drilling and production targets due to the failures in the drilling waste injection process represents high risks that demand sound engineering processes to ensure injection assurance.This paper describes the solution and detailed pressure monitoring methodology implemented to maintain safe injection assurance via regular disposal fracture diagnostics. Timely identification and a thorough evaluation of non-ideal pressure signatures observed during injection and post shut-in periods provided critical information required to detect subsurface anomalies. This can be an effective tool for the subsurface risks identification and characterization.The application of comprehensive fracture-mapping techniques is a major step in mitigating the environmental risks posed by waste. Waste mapping represents valuable information, not only in the overall planning of drilling operations, but in the fundamental and invaluable need to provide sound engineering for waste location and fracture containment assurance, thus minimizing environmental impact. Previous, oversimplified interpretations of multiple fracturing systems (or so-called uniform disposal domain) and new fracture initiation process are demonstrated to be in apparent conflict with fracture mechanics, stress calculations and the general principles of physics.The authors also describe the results of pressure analysis conducted in a North Sea injection well, which simultaneously was used for production. The well was utilized successfully for Cuttings Re-Injection (CRI) and for the disposal of produced water. The success of the operation was a direct result of close monitoring of key injection parameters and indepth analysis of injection pressure, despite risky geological conditions. Abnormal pressures increases and restrictions observed during injection were mitigated and addressed via a proper root-cause engineering and sound pressure diagnostic process. The drilling waste injection took place below a 13 3/8-in. casing shoe through the B annulus, in an open-hole section at the depth of 1220m TVD with a 24 0 deviation in the injection interval. The injection took place in close proximity to a major fault axis.

Deep Underground Injection of Waste from Drilling Activities—An Overview

“…Besides all that was mentioned above, subsurface injections of drilling waste makes the continuous use of oil-based mud during drilling troubled shale formations in environmentally sensitive areas possible [25]. Deep underground waste injections (cutting reinjection (CRI) or downhole waste injection (DWI)) are still the most economic methods for the disposal of waste generated through exploration and production activities in comparison with other available waste disposal methods [26,27]. For example, in the period of two years (concluded by March 2000), in Port Fourchon (Louisiana), more than 160,000 m 3 of waste produced by drilling and production activities containing naturally occurring radioactive materials (NORM) has been injected into a single well with an average cost of $119.5 per cubic meter of waste material, which is far less in comparison with the off-site waste disposal, with an estimated cost of $629 per cubic meter of the same waste material [18].…”

“…Although the annular waste injection method provides an opportunity to inject waste into exploratory wells and wells being drilled without interrupting the production or the drilling process (as is often the common practice in the North Sea region), in more than 80% of cases, operators selected the tubing injection method for their projects [26,46,49]. The main reason for this can be found in the adaptability of the tubular waste injection method, unlike annular waste injection, where the waste injection is a mandatory part of the initial well design.…”

“…Waste slurry is a homogeneous mixture of different kinds of waste collected during drilling and well completion activities (cuttings, used drilling fluids, contaminated rainwaters, scale, produced sands and clean up waste); water (regular or sea) and different additives [26,54]. Small amounts of additional waste generated at the rig site like glass, paper, pallets, plastics, rope, etc.…”

“…Similarity and differences between these two downhole injection methods in the oil and gas industry are presented in Table 8. As in the case of a reservoir stimulation through hydraulic fracturing, the quality of the created model and simulation strongly depends on accessibility and reliability of geological and operational information, as well as its improvement with additional information during the implementation of the project [26,77]. The required input information about the geological formation which is being considered for waste slurry injection can be obtained from wireline logs, well testing or through special petrophysical laboratory methods applied to core samples with reference to their reliability [39].…”

“…Microseismic is a pretty accurate method for defining the main fracture and its propagation but with a limited possibility of the differentiation in downhole seismic events from different sources (for example, propagation of the same fracture or creation of branches and fissures). This problem can be eliminated by adding different materials which create noise (detonation) in the main fracture during the injection or shut-in period [26]. Utilization of different radioactive tracers in waste slurry and an appropriate logging program may be very useful in the determination of the disposal domain, especially in the determination of injection points and their changes during the lifetime of the project [40].…”