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Abstract Sustainable Annulus Pressure (SAP) is a major safety and cost issue for Zakum Development Company (ZADCO) directly impacting it's ongoing development program and strategy. As part of its field development plan, ZADCO is in the process of horizontalizing many of its older deviated and vertical wells. During the well re-entry process, significant numbers of high outer annulus pressure cases are encountered. Attempts to remedy the situation using remedial cement squeezes are rarely successful, leaving a more complicated well, slowing drilling activity and occasionally resulting in abandonment of the well. A robust diagnostic and monitoring program lead to the conclusion, many high annulus pressure instances were due to thermal effects on fluids trapped in cement channels behind casing 1. Introduction ZADCO is in process of carrying out its field development program:changing existing deviated injectors or oil producers to horizontal wells, changing the distance between producer and injector wells, converting oil producers to water injection wells. As the number of re-entry wells increased, a significant number of high outer annulus pressure cases were encountered. High annulus pressure often appears during the well killing process, casing pressure testing, while squeezing off existing perforations, and in the majority of cases while milling the existing liner or during the drilling the new side track hole. To cure outer annulus pressure problems, ZADCO's usual approach was to establish a new barrier by creating holes in the production casing string and attempting to place cement behind it. Concerns with this approach were; during the well's production phase annulus pressure may build below the cement squeeze either breaking the cement, collapsing the inner 9 5/8" casing, or bursting the outer 13 3/8" casing. Often an annulus pressure problem appeared solved, only to have it reappear when the well was put back on production. These remedial jobs negatively affected the well completion strategy, creating complications in well completion equipment, well productivity and further well bore approach. A new methodology was needed to deal with these conditions. No Perforation Approach Experiencing a poor success rate curing high outer annulus pressure by conventional cement squeeze remedial jobs, ZADCO's Well Integrity Team decided on a new approach. Now the focus is on keeping the integrity of the production casing intact, avoiding perforations in the casing if at all possible. Candidate wells for the no perforation approach have the following characteristics:Good cement barrier above reservoir as determined by cement log evaluation. Outer annulus pressure behavior shows a declining tendency after successive bleed downs. Outer annulus effluent (oil or water) volume declines with each successive bleed off. A relationship is evident between activity in the wellbore and annulus pressure behavior and effluent recovery.
- Asia > Middle East > UAE > Abu Dhabi Emirate > Arabian Gulf (0.15)
- Asia > Middle East > UAE > Abu Dhabi Emirate > Abu Dhabi (0.15)
- Well Drilling > Casing and Cementing > Casing design (1.00)
- Well Completion (1.00)
Controls on Vertical and Horizontal Flow in a Carbonate Reservoir that Impact Gasflooding and Waterflooding
Thawer, Roxy (ADMA-OPCO) | Alhendi, A. (ADMA-OPCO) | Al Mazroui, Y. (ADMA-OPCO) | Boyd, Doug (ADMA-OPCO) | Masuzawa, T. (ADMA-OPCO) | Sugawara, Y. (ADMA-OPCO) | Hollis, C. (ELResLab) | Lowden, B. (ELResLab)
Abstract Identifying the location and quantification of flow units is critical to managing a reservoir's production and achieving maximum recovery. Gas injection is planned in a limestone reservoir offshore Abu Dhabi. To understand the benefits of future full field gas flooding, a pilot covering three reservoir units is underway. Ten wells were drilled and significant log/core data acquired. Interference tests within a reservoir unit in single wells and between-wells have revealed useful insights into the vertical and lateral continuity of barriers and conduits to flow. Recovery efficiency is driven by these contrasts in the reservoir sublayers. Significant variations in permeability occur over short vertical distances due to local facies and diagenetic changes, including dissolution events, distorting associations between porosity and permeability. Porosity cannot predict permeability to better than 1.5 decade on a logarithmic scale in this reservoir. Experimenting with NMR, Stoneley wave responses on one well, we were able to improve our predictive capabilities by combining the strengths of each tool. Predicted values fell mostly within half a log cycle of the whole core measurements. Vertical interference testing with a multi-probe Modular Dynamic Formation Tester (MDT?) used in a totally new way and using single well numerical models, proved useful in defining vertical barriers to flow. Cross-well interference testing proved that some of these barriers are discontinuous and act as baffles. Mobilities obtained from the MDTs, mimicked permeability contrasts measured in core. These contrasts confirmed the rapid response time seen in the cross-well interference tests. A full field simulation model with local grid refinement was able to match the cross-well interference test data. The integration of core description, whole core/plug physical properties, downhole electrical images, NMR, conventional logs, mobility, down-hole vertical as well as cross-well interference tests is presented and their impact discussed. Introduction Three gas injection pilots are commencing in three reservoir units (A, B & C) of this giant Middle East limestone field, currently under mature waterflood. The size of the pilots themselves could equal a full field development in many medium sized fields world-wide. Ten new wells and 10 existing ones form part of the pilot with well-spacing being generally 1km. The objective is to evaluate the benefits of gasflooding under secondary and tertiary conditions. This will allow major investment decisions to be made in the long-term full field development plans. One of the key uncertainties in gasflood performance is reservoir sweep. Vertical barriers and lateral conduits will control reservoir sweep and how well the injected gas can recover much of the remaining oil. Since there is no evidence of fractures in core where the pilots are targeted, the flow descriptions begin with predicting matrix permeability at the wellbore. This is extremely difficult in carbonate reservoirs and many attempts in the past have failed. However with suitable integration of all the static and dynamic data and careful upscaling to retain the contrasts described, it is possible to be predictive with a better level of confidence than previously experienced in this field. Observations on core permeability contrasts using core description and logs are extended to non-cored wells. At the wellbore vertical barriers are confirmed with MDT vertical interference testing. Lateral continuity of these barriers is not supported by inter-well interference measurements. This paper reports on the findings from the largest of the three pilots, Pilot C (6 new wells and 6 existing ones). The discussion however extends into the upper reservoir zones in the same wells. Even though the gas pilots in those zones are 5 km away, the trends seen are similar. The detailed core description is focussed on one key observer well Z16. Lateral trends are discussed briefly using other well data.
- Asia > Middle East > UAE > Abu Dhabi Emirate > Abu Dhabi (0.34)
- North America > Canada > Alberta > Clearwater County (0.24)
- Research Report (0.54)
- Overview (0.34)
- Geology > Sedimentary Geology (1.00)
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock > Limestone (0.45)
- Geophysics > Seismic Surveying (1.00)
- Geophysics > Borehole Geophysics (1.00)