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Abstract Scale formation has been a persistent challenge in many sour gas wells producing from one of the world's largest gas reservoir in Saudi Arabia. Accumulation of scale deposits on downhole tubular and in wellhead manifold interferes field operation, limits well accessibility and decreases well productivity. Extensive efforts have been devoted to understand the scale formation process and to develop cost-effective mitigation strategy. This paper discusses the up-to-date knowledge on the scale formation in these prolific gas wells and presents the descaling technologies deployed and currently considered. Scale composition analyses have been performed for a large number of deposits collected during well workovers and interventions. Wide range of mineral phases were identified and their distribution showed significant variations with samples. Scale often consisted of several different mineral phases. Iron sulfides were usually the dominant components, these included pyrrhotite, troilite, mackinawite, pyrite, marcasite and greigite. Ferric iron scales, such as hematite, magnetite, akaganeite, goethite and lepidocrocite, were also common in the scale mixtures. Common mineral scales, especially calcite, were often found. In addition, iron carbonate and other ferrous iron compounds were also identified. The relative abundance of these minerals showed wide-ranging variations from well to wells. Those variations also changed and with depth and time in the given wells. A more interesting phenomenon was the layered structure in the scale deposits, with two distinct layers having very different compositions. These results provided critical information for the understanding of scaling formation process. Scale removal with chemical method had limited success in past. Scale dissolvers, based on HCl acid, caused severe tubular corrosion and formation damage. Different mechanical techniques have been tested and implemented over the years. These field experiences are reviewed in the paper. Also, challenges and requirements for scale dissolvers are discussed.
- North America > United States (1.00)
- Europe (0.93)
- Asia > Middle East > Saudi Arabia > Eastern Province (0.28)
- Research Report > New Finding (1.00)
- Research Report > Experimental Study (0.93)
- Asia > Middle East > Saudi Arabia > Eastern Province > Al-Ahsa Governorate > Arabian Basin > Widyan Basin > Ghawar Field > Lower Fadhili Formation (0.99)
- Asia > Middle East > Saudi Arabia > Eastern Province > Al-Ahsa Governorate > Arabian Basin > Widyan Basin > Ghawar Field > Khuff D Formation (0.99)
- Asia > Middle East > Saudi Arabia > Eastern Province > Al-Ahsa Governorate > Arabian Basin > Widyan Basin > Ghawar Field > Khuff C Formation (0.99)
- (7 more...)
Abstract Many Khuff reservoir gas wells in Saudi Aramco fields are classified as sour producers with H2S levels as much as 8 mol% and CO2 contents as much as 5 mol%. Despite being completed with carbon steel tubular, corrosion failure has not been a major issue even after more than 20 years of service. On the other hand, most wells are experiencing scale buildup in production strings, causing an estimated production loss of up to 7 MMscfd for some wells. Besides, scale deposits are limiting well access for downhole surveillance and intervention. Significant efforts have been taken to understand the scale formation mechanisms. Extensive scale samples have been collected and characterized over the years. Although the exact chemical compositions change from well to well and also vary with depth in a given well, the scale deposits are usually mixtures of many compounds and often dominated with iron sulfide minerals. These iron sulfides include pyrrhotite, troilite, mackinawite, greigite, pyrite and marcasite. Other iron containing compounds, such as iron oxide and iron carbonate, are also found in significant amounts in most cases. Additionally, mineral scales, such as calcium carbonate and barium, strontium and calcium sulfate, are often present. Both mechanical and chemical methods have been applied for scale removal. Chemical dissolvers based on concentrated hydrochloric acid have been the most effective solvents. This types of dissolvers are very corrosive to well completion metallurgy at elevated temperatures, and the spent acids can cause severe formation damage due to re-precipitation of iron sulfides, if entering the near wellbore area. The rapid generation of large amounts of H2S gas creates a potentially lethal health hazard. This paper presents an effort to identify alternative dissolvers with high dissolving power and low corrosivity to carbon steel.
- North America > United States (1.00)
- Asia > Middle East > Saudi Arabia > Eastern Province (0.28)
- Energy > Oil & Gas > Upstream (1.00)
- Government > Regional Government > Asia Government > Middle East Government > Saudi Arabia Government (0.55)
- Materials > Chemicals > Commodity Chemicals > Petrochemicals (0.34)
- Asia > Middle East > Saudi Arabia > Eastern Province > Al-Ahsa Governorate > Arabian Basin > Widyan Basin > Ghawar Field > Lower Fadhili Formation (0.99)
- Asia > Middle East > Saudi Arabia > Eastern Province > Al-Ahsa Governorate > Arabian Basin > Widyan Basin > Ghawar Field > Khuff D Formation (0.99)
- Asia > Middle East > Saudi Arabia > Eastern Province > Al-Ahsa Governorate > Arabian Basin > Widyan Basin > Ghawar Field > Khuff C Formation (0.99)
- (6 more...)
Abstract Various mechanisms can lead to the formation of iron sulfide scale in formations, tubing, downhole equipment, and surface facilities. However, all of these mechanisms essentially require a source of hydrogen, sulfide, and iron. Hydrogen sulfide (H2S) can result from sulfate reducing bacteria, thermal decomposition of sulfate, or oil decomposition. Iron sulfide (FeS) species can cause numerous operational problems, well productivity and injectivity loss. The physical appearance and texture of iron sulfide scale depends on well type. Scale removal techniques must be quick and non-damaging to the wellbore, tubing, and formation. Equally important, they must not cause re-precipitation. Current industry practices in scale removal often involve mechanical tools and chemical dissolvers. Chemicals are often the first to be considered due to lower cost, particularly when scale is not easily accessible or exists where conventional mechanical removal is ineffective. This paper discusses extensive efforts in the development of products to effectively remove iron sulfide scale at high temperatures and pressure without H2S generation. Scale samples were collected from various oil and gas wells. The mineralogy and elemental composition of samples were determined using x-ray diffraction (XRD), x-ray fluorescence (XRF), and scanning electron microscope (SEM) equipment. Tests were conducted to evaluate the iron sulfide dissolution capability at 250ยฐF. The selected dissolvers are designed to reduce operational risk, increase dissolution, and reduce the risk of corrosion problems. Lastly, a brief summary is presented discussing efforts made to develop a reliable FeS scale inhibitor as a sustainable solution for the continued development of sour reservoirs.
- Europe (0.69)
- Asia > Middle East > Saudi Arabia (0.48)
- Asia > Middle East > Saudi Arabia > Eastern Province > Al-Ahsa Governorate > Arabian Basin > Widyan Basin > Ghawar Field > Lower Fadhili Formation (0.99)
- Asia > Middle East > Saudi Arabia > Eastern Province > Al-Ahsa Governorate > Arabian Basin > Widyan Basin > Ghawar Field > Khuff D Formation (0.99)
- Asia > Middle East > Saudi Arabia > Eastern Province > Al-Ahsa Governorate > Arabian Basin > Widyan Basin > Ghawar Field > Khuff C Formation (0.99)
- (48 more...)
Iron Sulfide Scale Dissolver for Downhole Application: Where Are We Now?
Wang, Qiwei (Saudi Aramco) | Chen, Tao (Saudi Aramco) | Chang, Frank F. (Saudi Aramco) | Nasser, Waleed Al (Saudi Aramco) | Shen, Shouwen (Saudi Aramco) | Al-Badairy, Hameed (Saudi Aramco) | Zaidi, Syed (Saudi Aramco) | Liang, Feng (Aramco Services Company: Aramco Research Center-Houston) | Leal, Jairo (Saudi Aramco) | Syafii, Irfan (Saudi Aramco) | Al-Mukhles, Amro (Saudi Aramco)
Abstract Downhole scale deposition in the Khuff sour gas wells in Saudi Arabia has been a persistent problem, which negatively affects operation and production. Scale deposits are composed of predominantly iron sulfides with other types of minerals also present. Mechanical descaling treatment, although expensive and time-consuming, is often required. Effective scale dissolver is highly desirable to enhance descaling efficiency and to reduce treatment cost. An ideal dissolver is required to have high scale dissolving power, no damage to downhole completion and well productivity, and minimal H2S liberation. This paper presents the laboratory studies on the new scale dissolvers developed by service companies. These products have pH values ranging from strong acidic (pH < 2) to high alkaline (pH > 12). Dissolvers were evaluated for thermal stability, corrosivity to mild steel, and compatibility with formation water at downhole temperatures. The potentials of iron sulfide re-precipitation in spent solutions and free H2S generation were also examined. The qualified chemicals were then evaluated for their dissolving capacity using authigenic pyrrhotite and field scales at elevated temperatures. The obtained results show that most effective acidic dissolvers evaluated in this study were very aggressive to low alloy carbon steel at downhole temperatures. For these with acceptable corrosivity, formation of iron sulfide reprecipitation in spent dissolvers and the generation of a large quantity of free H2S gas also prevented them from field application. Some dissolver products were disqualified due to incompatibility with formation water. Dissolvers with near neutral and alkaline pH values, in general, were inefficient to dissolve the heterogeneous iron sulfide scales. The performance of tested dissolvers varied with scales from different wells, attributed by differences in composition, microstructure, and the presence of hydrocarbon. Results also suggested that pyrite and marcasite were possibly formed during the dissolution process. This paper presents an objective assessment on the currently available iron sulfide scale dissolvers, highlights the challenges on downhole scale dissolution in high temperature sour wells, and provides new insights on the scale dissolution process. The results suggest that further R&D efforts are required to develop more effective chemical solutions to mitigate the iron sulfide scale problem.
- North America > United States (1.00)
- Asia > Middle East > Saudi Arabia > Eastern Province (0.28)
- North America > United States > Texas > Permian Basin > Yeso Formation (0.99)
- North America > United States > Texas > Permian Basin > Yates Formation (0.99)
- North America > United States > Texas > Permian Basin > Wolfcamp Formation (0.99)
- (22 more...)
Analysis of Deposition Mechanism of Mineral Scales Precipitating in the Sandface and Production Strings of Gas-Condensate Wells
Franco, C.A.. A. (Saudi Aramco) | Solares, J.R.. R. (Saudi Aramco) | Al-Marri, H.M.. M. (Saudi Aramco) | Mukhles, A.E.. E. (Saudi Aramco) | Ramadhan, N.H.. H. (Saudi Aramco) | Saihati, A.H.. H. (Saudi Aramco)
Summary Thick deposits of various types of mineral scales are presently forming in the tubulars and formation of gas producers drilled in Saudi Arabian carbonate reservoirs. These mineral scales precipitate when ideal thermodynamic conditions combine with dissolved minerals present in formation waters. Without remedial action over time, these deposits can grow thicker and end up plugging tubulars and the reservoir. Thick deposits of mineral scales have recently begun to appear in gas producers in certain areas of the field. A comprehensive study was conducted to ascertain the nature of the precipitation mechanism and identify potential solutions to the problem. This paper details how laboratory analysis data, well production history, reservoir geology and petrophysics, and reservoir description were analyzed and used with sophisticated computer software to identify the formation-damage mechanism and the different scale types precipitating in the wellbore and formation. Extensive simulation work was conducted as part of the study to forecast the type and amount of mineral-scale precipitation that can be anticipated at varying reservoir and producing conditions. The study also evaluated the most cost-effective and feasible ways to remove different types of scale deposits. The future scale-inhibition and -removal strategies to be implemented in existing and future gas producers are being derived in large part from the results of the study described in this paper.
- North America > United States (1.00)
- Asia > Middle East > Saudi Arabia (0.70)
- Asia > Middle East > Saudi Arabia > Eastern Province > Al-Ahsa Governorate > Arabian Basin > Widyan Basin > Ghawar Field > Lower Fadhili Formation (0.99)
- Asia > Middle East > Saudi Arabia > Eastern Province > Al-Ahsa Governorate > Arabian Basin > Widyan Basin > Ghawar Field > Khuff D Formation (0.99)
- Asia > Middle East > Saudi Arabia > Eastern Province > Al-Ahsa Governorate > Arabian Basin > Widyan Basin > Ghawar Field > Khuff C Formation (0.99)
- (5 more...)