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Hao, Hongda (China University of Petroleum) | Hou, Jirui (China University of Petroleum) | Zhao, Fenglan (China University of Petroleum) | Wang, Zhixing (China University of Petroleum) | Fu, Zhongfeng (China University of Petroleum) | Li, Wengfeng (China University of Petroleum) | Wang, Peng (China University of Petroleum) | Zhang, Meng (China University of Petroleum) | Lu, Guoyong (China University of Petroleum) | Zhou, Jian (China University of Petroleum)
As an effective method for resource utilization, CO2 huff-n-puff can be utilized to reduce CO2 emissions and enhance oil recovery in edge-water flock-block reservoir, which was implemented in Jidong Oil Field, China since 2008 with oil production of 6.5×104 bbls by 2015. During operation period, synergetic effect was observed in adjacent wells with water cut drops and oil increments in a horizontal well group. Experimental and numerical simulations were conducted to investigate synergetic mechanisms of CO2 huff-n-puff. 3D physical models with a horizontal well group and edge-water-driving system were established in laboratory to simulate the edge-water fault-block reservoir. The formation mechanisms and influence factors of synergetic CO2 huff-n-puff were studied through laboratory experiments. Base reservoir model was also built to further discuss the synergetic types and injection allocations for CO2 huff-n-puff in horizontal well group.
Synergetic CO2 huff-n-puff is a smart gas cycling strategy for the horizontal well group to balance the formation pressure and replace the interwell oil. Experimental and numerical results showed that after CO2 injected into low tectonic position of the reservoir, synergetic effect could be observed in high position well with water cut drops and oil increments. The mechanisms of synergetic effect can be recognized as formation energy supplement, gas sweeping, gravity segregation and CO2-assisted edge-water driving. The stratigraphic dip and heterogeneity are advantages for the formation of synergetic effect. The synergetic types of CO2 huff-n-puff can be summarized as single-well synergy and multi-well synergy. For single-well synergy, edge-water invasion can be effectively controlled by energy supplement after CO2 injected into relatively low position well. For multi-well synergy, better synergetic effect and remaining oil replacement can be achieved after gas injected through different positions of the well group. The development efficiency of synergetic CO2 huff-n-puff can be enlarged with 700t CO2 injected into low position well + 100t CO2 into high position well, and about 5767.9 bbls oil of the well group could be recovered with the soaking time of 50d.
Carbonate sands are encountered in several locations where offshore petroleum activities are underway, in particular the Southern Mediterranean Sea, the Persian Gulf, the Red Sea, Florida, Brazil, India, the Philippines and Australia. Problems have been encountered in the Arabian Gulf where driven piles were observed to free fall through carbonate sand. Further pile installation difficulties were observed in Australia, Philippines and Brazil, due to the low skin friction developed by the driven piles. In these soil types drilled-and-grouted piles are therefore preferred. The MIDOS (MIxed Drilled Offshore Steel) pile is a new type of offshore pile, successfully installed in an onshore field trial in silica sands. The feasibility of this pile in calcareous (or carbonate) sediments was extensively conducted in a laboratory scale investigation, as part of a joint research project between BAUER Maschinen GmbH and University College Dublin (UCD). Two tests materials were used for this study: carbonate sand from Dog’s Bay beach and silica sand from Blessington (both from Ireland). Preliminary mineralogical and geotechnical tests are shown in this manuscript. XRD and SEM analysis have been performed to assess the materials from a chemical and mineralogical point of view. XRD results revealed that the Dog’s Bay sand consists of at least 80% calcium. Grain size distribution, void ratio measurement and direct shear tests for silica and carbonate sands have been carried out. The basic geotechnical properties of the carbonate sand from this study are compared in this paper with the geotechnical data available for other carbonate sediments worldwide. The MIDOS pile is also briefly described as a novel offshore drilled-and-grouted pile, which is developed specifically to cope with such challenging ground conditions.
Water Shut-Off in Oil Production Wells - Lessons from 12 Treatments.
In the past few years water shut-off treatments in production wells have started to become accepted as part of standard well service work. The benefits from a successful treatment can be large and immediate; often the "pay-back" time for a water shut-off job is just a few months, weeks, or even days. This paper details the lessons learnt from BP's first twelve "modern" production well water shut-off treatments in Alaska and the North Sea, carried out over the last three years.
Three types of treatment will be discussed:
- Near well bore, total shut-off of an isolated zone. Here one entire section of well bore is being abandoned in order to allow production from other zones.
- Injecting a relative permeability modifier, full well bore, into all perforated zones. In this case it may not be possible to identify the specific water producing zone, or there may be no barriers (such as shales) beyond the near well bore region to provide fluid control (of both the treating fluid and subsequent produced fluids).
- Dual injection treatments. In this final category, a single, discrete, reservoir zone is targeted (for either total shut-off or relative permeability modification), but mechanical well bore control of fluid placement is not available.
Detailed, example, case studies will be presented for each category of treatment, together with a discussion of how to apply the treatments to a range of reservoir conditions.
Water Shut-Off (WSO) treatments in production wells are a routine part of standard well service work. We now use cement squeezes or mechanical isolation methods with high success rates for "straightforward" WSO targets. By contrast, the perception of chemical treatments such as polymer gels for WSO has been one of relatively high risk. Therefore we have tended to use gel-based methods as a final option (short of side-tracking the well) for WSO when standard methods are obviously inapplicable or have already been tried without success. These target wells have been complex, and some had mechanical limitations due to long-term shut-in or failed previous WSO attempts using plugs or cement. We have often been exploring new territory, and have had to consider many issues.
Despite this, our experience since we restarted using gels in late 1993 has been very positive. The first six applications were all technical and economic successes. The conclusion so far is that with care a high success rate can be obtained with gel-based WSO, and this approach can often hit the parts other WSO methods cannot reach. As with any developing method, there are some potential problem areas. Some are chemistry-related, some are well-related and some reservoir-related. This paper deals with lessons learnt during design and application, and precautions and short-cuts we have found helpful. The lessons are drawn from 12 treatments, most of which (but not all) are mentioned specifically. These treatments were completed in collaboration with operating groups in BP Exploration and ARCO Alaska, Inc. There is still no comprehensive, how-to-be-safe manual as yet, but this at least brings together a partial check list.
However, this is certainly not a comprehensive check list. In particular, other oil companies and service companies have been enjoying recent success with very different versions of the same gel system, and with different chemistries altogether. Our job designs are conservatively based on systems that we know well enough to control. Other options might well be simpler, cheaper or technically more robust than the ones we have used for some of our targets. As users and adapters, rather than inventors, we will undoubtedly pick up new designs, especially for some of the non-conventional well targets on the horizon.
By discussing all we can think of in the way of job notes and alternative options we are aware that we may make the gel approach look complex and full of potential pit-falls. This comes from dealing with many very different intervention objectives. several chemical systems, and a vast range of well/reservoir conditions. The reality can be quick and easy.
The term "Travelling Cylinder" is used to describe a diagram employed in directional drilling on multi-well locations as an aid to collision avoidance. There are a number of variants and the differences between them can, if not properly appreciated, lead to a misinterpretation of the physical situation which, in turn, may put the drilling operation at risk.
During planning, and at the wellsite, the Normal Plane version of the Travelling Cylinder diagram is a powerful tool for collision avoidance due to its innate simplicity. Survey readings can be plotted on the diagram and an immediate visual assessment made not only of the trend of the well in relation to the plan but also relative to adjacent wells. The diagram can be used without recourse to computers. A major advantage of the Normal Plane diagram is that it provides an unambiguous method for displaying anticollision tolerances. With a minimum of interpretation the plot provides a simple and direct technique for go/no-go drilling decisions in potential collision situations. The Normal Plane diagram provides a robust and computationally efficient method for collision checking. Scanning down drilled wells against the plan, as opposed to checking down the plan against drilled wells, ensures that potential intersections are not missed.
Other versions of the travelling cylinder diagram based on the Horizontal Plane projection or a Closest Approach calculation should not be used for anti-collision applications because of a number of distinctive shortcomings.
Wells have routinely been drilled in close proximity to others using standard plan view and vertical section drawings. Sometimes wellsite personnel have encountered serious problems with the visualisation of true well separations and rates of convergence or divergence. That numerous wells have been drilled in this way without incident does not necessarily vindicate the practice. In some instances the difficulty of interpretation has reportedly been a contributory factor in subsurface collisions. An alternative method of displaying the information is necessary to improve safety in this type of operation.
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Offtake levels, under natural flow, from Thistle and Deveron wells A46(45) and A51(03) are both constrained by relatively poor pressure support. It was decided to install jet pumps in the existing completions to test the reservoir performance under artificial lift. If enhanced offtake levels could be supported permanent gas lift completions would be installed at a later date. In addition to this interim increases in the production rates would be achieved prior to workover.
A wireline retrievable jet pump, complete with a integral sub-surface safety valve (SSSV), has been designed for installation in the (open) sliding side door (SSD) of the existing completions. Power fluid, supplied from the water injection system, is routed via the casing-tubing annulus and returns are produced up the tubing string. Downhole isolation of both the tubing and the annulus is achieved by means of the annulus pressure operated SSSV which is located immediately below the jet pump.
The design procedure for the selection of the optimum nozzle/throat combination is described. Operating procedures have been developed to ensure successful operation of the device and details are given of both the downhole and surface hardware.
Results of actual field performance are presented and comparisons made with predicted values. Finally details are given of design modifications which were implemented in response to problems which developed during field trials.
The Thistle field, located in block 211/18a of the Northern North Sea, produces oil via a single, centrally located platform. Area 6 is located to the north of the main field and production is achieved via a single well A46(45). The Deveron field has separate field status and is located immediately to the west of Thistle. Deveron is produced via wells A51(03), A44(07) and A48z(23) drilled from the Thistle platform (Fig. 1).
Generally the Thistle main field has adequate reservoir pressure support to facilitate production under natural flow. However, the performance of certain areas of the main field, Area 6 and the Deveron field has indicated that artificial lift would be beneficial in specific wells. A previous study identified gas lift as the optimum artificial lift method and two wells are currently being gas lifted. Current plans envisage that a total of 7 wells will be gas lifted including Area 6 and Deveron wells A46(45) and A51(03).
Prior to committing to the installation of permanent gas lift completions in these wells, it was considered prudent to perform short term artificial lift trials to confirm that enhanced offtake levels could be sustained. The simplest and most cost effective way of achieving this was to employ jet pumps installed by wireline in the existing completions. If the trials indicated that enhanced production rates could indeed be sustained it would be beneficial to continue jet pumping in the interim pending installation of the gas lift completions. For this interim production period downhole closure was required. In response to this an integral jet pump/SSSV was developed which could be installed into the (open) SSD's of the existing completions.
The method adopted for pump sizing and details of an integral jet pump/SSSV assembly are presented in this paper. Field experience on two wells is described and comparisons made between actual and simulated performance. Details of the surface hook-up and jet pump operating procedures are also presented.
3 JET PUMP OPERATING PRINCIPLES
The theory of jet pumps has been adequately documented (Ref. 1). In summary the jet pump is a fluidic device.