Fakhreldin, Yasser Elmoghazy (PDO)
Fakhreldin, Yasser Elmoghazy (PDO)
Petroleum Development Oman, PDO, is planning to improve ultimate recovery of condensate from a retrograde condensate gas field by reducing the rate of reservoir pressure decline. This shall be accomplished by re-injecting into the reservoir some of the produced gas and all of the acid gas extracted from the sweetening process. The composition of the injected gas will vary over time, from 15% CO2 and 3% H2S to 56% CO2 and 10% H2S. These combinations of CO2 and H2S can cause the wells cement to deteriorate. Portland cement tends to strongly degrade once exposed to such acid gases by reacting with calcium hydroxide formed from hydrated calcium silicate phases. As carbonates are dissolved in a low pH environment, the cement-carbonation products will not act as a self-plugging agent / s in the cement sheath. The resulting decrease of compressive strength and increase of permeability could lead to loss of zonal isolation and casing corrosion. These requirements led PDO to investigate and trial CO2- resistant cement to enable zonal isolation and ensure long term containment of the reservoir fluids. The nominated new technology cement system was trailed in a deep gas well which penetrated a reservoir which has high concentrations of CO2 and H2S at a super critical condition. The CBL/VDL log which was run after well completion showed excellent results. The well-cement quality shall be re-logged prior to any zonal shutoff work-over or well decommissioning. This paper will discuss the design, execution, and evaluation of the first acid gas resistant cement in PDO in one of the high profile gas well in South of Sultanate of Oman.
Fakhreldin, Yasser Elmoghazy (Petroleum Development Oman)
Removing filter-cake is essential for reducing the formation damage caused by drilling activities in various production and injection wells. These filter-cakes typically contain bio-polymers such as xanthan gum, poly-anionic cellulose, starch, along with bridging agents such as sized calcium carbonate particles. A novel chemical series was applied in laboratory tests; it perfectly degrades the filter cakes. Different performance tests showed that the filter cake was entirely removed after being treated with the novel chemical series. A direct reaction between the drilling mud and the novel compounds resulted in a complete loss of mud viscosity. Encouraged by the above data; core flood analysis were performed to test the effectiveness of the novel compounds on sandstone cores. The scenarios, which might occur in field applications, were simulated in the laboratory under controlled conditions and the responses of the core samples under these conditions were measured. Return permeability were approximately 100% after treatment with the new compounds. There was no swelling of the interstitial clay component of the formation plugs over a remarkable duration of time and wide range of temperatures.
Well-bore cleaning becomes an integral part of well completion operation, aiming to maximize well productivity from near well - bore. The awareness becomes more widespread with more and more horizontal and sand packed open-hole wells drilled with non- damaging drill-in-fluids. The drill-in fluids were composed of starch and / or cellulose polymers, xanthan polymer and sized calcium carbonate. Insufficient degradation of the filter-cakes can significantly impede the flow capacity at the near well-bore area. Classical clean up materials such as acids, oxidizers, and enzymes are used as well-bore cleaning fluids; α-amylase and α, β- amylase have been selected by Petroleum Development Oman (PDO) as the most effective means for cleaning up the filter cake deposited by a water- based mud on wells completed with open hole completion. PDO considered the enzymes as the best filter cake breaker despite all its drawbacks.1
Al-Kitany, Najim Abdulla (Petroleum Development Oman) | Ghosh, Bisweswar (Petroleum Institute) | Fakhreldin, Yasser Elmoghazy (Petroleum Development Oman) | Bemani, Ali S. (Sultan Qaboos University) | Al-Hadrami, Hamoud Khalfan H. (Sultan Qaboos University) | Al-Wahaibi, Yahya Mansoor (Sultan Qaboos University)
Wellbore clean up has become an integral part of well completion operation aiming to maximize well productivity from a near skinless wellbore. The awareness has become more widespread with more and more horizontal and sand packed openhole wells being completed with so-called non damaging Drill-In-Fluids (DIF). Although drill-in-fluids control fluid loss and saturation related damage to a great extent, they tend to leave a sticky filter cake containing polymers and Calcium Carbonate particulates which can severely restrict well flow. Acids, oxidizers, chelating agents and enzymes have been often used as wellbore clean up fluids with mixed success. This article demonstrates laboratory and field evidences on superior efficiency of some recently developed bio-enzymes and explains the reason of their not so satisfactory treatment result in some wells.
Simulated Reservoir Condition Core Flow (RCCF) and return permeability measurement was the basis of laboratory evaluation and comparison of various clean up formulations, including inorganic/organic acids, oxidizing agents, various enzymes and combination treatments. Mud filter cake was developed by simulating drilling and reservoir parameters. Cleaning treatments were mimicked as per realistic field operation. Photographic evidences were produced on clean up efficiency and final conclusion was drawn based on return permeability.
Well treatment methodologies are discussed and production data from over twenty wells/legs were produced, analyzed and compared. An effort is made to analyze unsatisfactory treatment outcome in some of the enzyme treated wells and to establish the best practice approach for wellbore clean up operations.