Copyright 2012, SPE/APPEA International Conference on Health, Safety, and Environment in Oil and Gas Exploration and Production This paper was prepared for presentation at the SPE/APPEA International Conference on Health, Safety, and Environment in Oil and Gas Exploration and Production held in Perth, Australia, 11-13 September 2012. This paper was selected for presentation by an SPE/APPEA program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been reviewed by the Society of Petroleum Engineers or the Australian Petroleum Production & Exploration Association Limited and are subject to correction by the author(s). The material does not necessarily reflect any position of the Society of Petroleum Engineers or the Australian Petroleum Production & Exploration Association Limited, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Society of Petroleum Engineers or the Australian Petroleum Production & Exploration Association Limited is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of SPE copyright.
White, Adrian (Geo Mechanics International) | McIntyre, Brett (Apache Energy) | Castillo, David (GeoMechanics International) | Trotta, Julie (GeoMechanics International) | Magee, Marian (GeoMechanics International) | Ward, Christopher D. (GeoMechanics International) | O'Shea, Paul (Apache Energy)
A post-mortem analysis of the Gnu-1 well was conducted to help us to understand drilling experiences in the context of the pore-pressure and stress profiles. The post-mortem involved a review of the drilling experiences and an analysis of CAST image data, wireline-log data, and the logging-while-drilling (LWD) logs. This information was used to refine and verify a geomechanical model (in-situ stress, pore pressure, and rock-mechanical properties) in the vicinity of the Gnu-1 well. Of prime concern was the verification of the predrill pore-pressure prediction previously undertaken using 3D-seismic-velocity data and offset-well data. Wellbore-failure and natural-fracture analyses were integral parts of the post-mortem. Wellbore breakouts seen in the image data allowed the pore pressure in the 8.5-in. hole section of Well Gnu-1 to be constrained. Modeling using image data collected in the Athol formation indicates that the pore pressure does not increase as rapidly as was estimated in the predrill study. Pore pressures in the North Rankin formation and below were consistent with the predrill study. The geomechanical model was able to explain the losses seen in the Athol formation in Well Gnu-1 when using the mud weights experienced by the open hole at the time of drilling.
The Gnu prospect is situated in the northern portion of Block WA-209-P in the Dampier subbasin, Australian northwest shelf (Fig. 1). The prospect is located within the Reindeer gas field. A number of offset wells exist in the region, the closest wells being Well Reindeer-1 (approximately 1.5 km to the northeast) and Well Caribou-1 (2 km to the southeast).
Well Gnu-1 was designed as an exploration well. The anticipated overburden stratigraphy at the location of Well Gnu-1 consists of Tertiary and Upper Cretaceous carbonates, marls and siltstones that overlie Cretaceous claystones, siltstones and minor sandstones, and greensands. The primary aim was to drill vertically to intersect the Muderongia australis glauconitic sandstone and then to build angle and continue drilling a deviated hole through the main Reindeer field gas appraisal within the Legendre formation and into the North Rankin, Brigadier, and Mungaroo formations.
A new thermal recovery scheme is proposed that utilizes Steam-Assisted Gravity Drainage (SAGD) well pairs as well as Cyclic Steam Stimulation (CSS) wells placed in between the SAGD well pairs. The wells are operated in CSS mode until the steam chambers are in contact with each other and then switched to SAGD operation. It is shown that the new process recovers greater amounts of bitumen with lower injected steam in shorter operation time than is achieved with SAGD, Fast-SAGD and CSS.
The JV operator was looking for a combination of technologies to optimize drilling in Canada's Mackenzie Delta region. The area is characterized by a permafrost section up to 2,000 ft (609 m) thick. This shallow permafrost section is dominated by unconsolidated silt with freshwater ice ranging from 60% volume to pure ice layers. Historically, mechanical heat input has melted the frozen layer, resulting in increased hydrates/shallow gas risks, extreme hole enlargement/cleaning problems, rig support issues, wellbore instability, stuck pipe, hydraulic isolation, and environmental impact issues.
Optimizing drilling operations through the shallow section is critical to maximize the number of wells that can be drilled with the available rigs in this limited-access area. To move the rig requires approximately 3 ft (1 m) of ice cover, which significantly limits the operating season, increasing the need for rig efficiency and reduction of non-productive time (NPT). The industry has endorsed the importance of mud cooling through the shallow permafrost and the underlying hydrate-bearing formations to avoid borehole instability and to control hydrate dissolution. However, the industry has struggled to maintain sufficiently cold mud at the high pump/power rates required to effectively drill/clean the larger surface holes.
To solve the challenges, the operator utilized a casing-while-drilling (CwD) and casing bit system with a unique-to-the-industry mud-chilling technology and a variety of controlled drilling parameters. The CwD and casing bit system allowed the operator to drill and set casing through the problematic zones in one operation with relatively low flow rates to avoid hole enlargement. The lower flow rates also enabled the use of smaller, lighter rig equipment that reduced the required ice thickness to move the rig and therefore increase the winter season operating period. Following the successful implementation of the CwD and casing bit system on the first well of a winter program, the second well was drilled safer with the elimination of a casing string, which further reduced drilling time and cost.
White, Adrian (Geo Mechanics) | Ward, Christopher D. (Geomechanics International Inc. GMI) | Castillo, David Andrew (Geomechanics International Inc. GMI) | Magee, Marian (Geomechanics International Inc. GMI) | Trotta, Julie (Geomechanics International Inc. GMI) | McIntyre, Brett (Apache Energy Ltd.) | O'Shea, Paul (Apache Energy Ltd.)
A postmortem analysis of the Gnu-1 well was conducted to help understand the drilling experiences in the context of the pore pressure and stress profiles. The postmortem involved a review of the drilling experiences, the analysis of CAST image data, wireline log data and the LWD logs. This information was used to refine and verify a geomechanical model (in-situ stress, pore pressure and rock mechanical properties) in the vicinity of the Gnu-1 well. Of prime concern was the verification of the pre-drill pore pressure prediction previously undertaken using 3D seismic velocity data and offset well data. Wellbore failure and natural fracture analysis were an integral part of the postmortem. Wellbore breakouts seen in the image data allowed the pore pressure in the 8½?? hole section of Gnu-1 to be constrained. Modelling using image data collected in the Athol Formation indicates that the pore pressure does not increase as rapidly as was estimated in the pre-drill study. Pore pressures in the North Rankin Formation and below were consistent with the pre-drill study. The geomechanical model was able to explain the losses seen in the Athol Formation in Gnu-1 when using the mud weights experienced by the open hole at the time of drilling.
Summary Audio-magnetotelluric (AMT) exploration is being evaluated as a tool for locating unconformity related uranium deposits in the Athabasca Basin in Canada. These uranium deposits are often located above graphitic basement conductors that can be located with electromagnetic (EM) methods. A test survey at the McArthur River Mine showed good agreement between the known location of the uranium deposit and that inferred from the AMT data. Electrical resistivity models derived by 2D inversion were validated by comparison with 3D inversion and correlation with well log data. This validation was also tested with 3D forward modeling and 2D synthetic inversions.
Our research shows that boron in the rock man Trix occrs in quantities large enough to affect seriously log analysis in several formations along the Texas Gulf Coast. Examples of log-derived quantities affected by boron content include porosity (compensated neutron log), gas indicator (crossover of neutron and density porosity curves), shale indicator (neutron-density crossplots used in shaley sand interpretations), water salinity and saturation (pulsed neutron logs), and elemental analysis (derived from energy spectrum of gamma rays of capture). Our study of cores from the Frio Formation indicated no obvious geographic correlation. There was a clear trend toward higher boron content in Frio shales and shaley sands than in relatively clean sands. Boron also occurs in significant amounts in mud constituents such as bentonite, barite, and lignosulfonate. Boron also occurs in Gulf Coast Frio formation waters, but this does not directly affect thermal neutron logs or pulsed neutron logs run soon after drilling, because these logs respond mainly to conditions close to the well, within the invaded zone, where little or no formation water is present. It may be possible to correlate boron in the formation water with boron in the rock, but a lot more data would be needed to establish such a correlation. A reliable epithermal neutron log would go a long way toward solving the boron problem, but epithermal logs to date have been too sensitive to borehole environment. An approach suggested recently by D. V. Ellis et al. offers some hope that the problem could be solved by simultaneous use of data from the compensated neutron and pulsed neutron logs, which are affected differently by the boron content of the formation. Again, more data are needed to validate this approach.
Boron is a chemical element and a light weight semimetal, with several of its properties listed below. Boron was discovered by H. Davy and, independently, by In its uncombined, elemental form, boron is used primarily in the metal industry. It has been well established in the numerous literatures on pulsed neutron logging that the tool response in shaly reservoir rock can be expressed as a function of the combined effect of the reservoir rock, its shale content, and type of water and hydrocarbons. The latter has a thermal neutron capture equivalent of 127 relative to NaCI. The paucity of boron in most limestones, ousually less than 20 ppm, has been well established.