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Collaborating Authors
Results
Evaluation of Alcohol-Based Treatments for Condensate Banking Removal
Alzate, Guillermo A. (U. Nacional de Colombia) | Franco, Carlos Alberto (BP Amoco Colombia) | Restrepo, Alejandro (BP Exploration Colombia Ltd.) | Del Pino Castrillon, Jessica J. | Barreto Alvares, Diogenes Laureano | Escobar Murillo, Alfaro Alberti
Abstract The use of stimulation treatments based on alcohol to remove liquid blockage or condensate banking in the near well zone date from sixties. Among the proposed mechanisms to explain the enhancement in gas effective permeability and also the higher degree of cleaning and liquid removal obtained in laboratory and field studies, are interfacial tension reduction and the miscibility characteristics reached between the treatment fluids and the formation fluids. This paper presents the results for compatibility and displacement tests carried out among reservoir fluids, alcohol and inhibited diesel based treatments and formation cores from main Cupiagua field. These tests are focused about the behavior of these treatments when they are applied in core flooding tests to reduce liquid saturation and also to increase the gas effective saturation in a porous media. The offered results can be interpreted as a preliminary sight about the use of these treatments on lab scale before applying them as stimulation fluids on a field project. The study consists in assess the alcohol-based and inhibited diesel treatments' efficiency through the gas effective permeability before and after of the treatment injection into a core. The objective was focused to study the use of alcohol and inhibited diesel to remove formation damage by liquid blockage and their application in condensate gas reservoirs. The alcohol-based treatments show consistent results about their effectiveness both on core tests carried on Mirador formation, Cupiagua Main Field - Colombia, and Berea sandstone. In general, the results show up an increase on the gas effective permeability, the lower the core permeability the higher the gas effective permeability enhancement reached after the treatment. The alcohol labeled 21-NE-06 and inhibited diesel treatments increase the gas effective permeability both in Berea and Mirador cores. Both Alcohol 21-NE-06 and inhibited diesel based treatments are effective for removing liquid phases that cause a liquid blockage to gas flow. The stimulation degree is higher in Mirador than in Berea cores. Some treatments did not show any stimulation degree, instead, they generate additional gas effective permeability impairment. Introduction The reservoirs of condensate gas had been subject of study with emphasis in last years because the growing participation of this kind of hydrocarbons in new reserves. Gas condensate reservoirs as a result of fluids' production process and related with the production rate magnitude diminish their pressure below the dew point pressure. This situation is more evident at near production wells' zone, where due to the reduction of radial gas flow area produces an additional pressure drop. Gas condensate reservoirs are very prompted to show up formation damage at the near well zone. [1–6] If the fluid flowing pressure is below of dew pressure, liquid drop-out accumulations would present in the reservoir, and in a higher degree near to the producing wells. It results in an increasing on reservoir liquid saturation what is called as formation damage by liquid blockage. This liquid blockage remains due to capillary forces and also due to the high gas-liquid mobility ratio. Some authors propose the existence of three flow's regions on gas condensate reservoirs, which appears sequentially or simultaneously along production time depending of pressure profile. When the flow pressure is higher than dew pressure, only exists gas flow. This region exists in any point of the reservoir where this condition is met, but its existence is evident at early production times. When the reservoir pressure drops below dew point pressure, fluid condensation results in the formation of liquid banking. In this region and at early time during liquid condensation process only exists gas flow due to temporal immobility of liquid. Near zone to producer's wells, where the pressure drop is higher and also when the condensation process last for longer times, the liquid saturation achieves mobility levels and then simultaneous flow of gas and condensate exists, Figure 1.
- South America > Colombia > Mirador Formation (0.99)
- South America > Colombia > Casanare Department > Llanos Basin > Cupiagua Field (0.99)
Abstract The well damage history in the fields operated by BP Colombia has showed an interesting performance in all producer and injector wells. The abnormal productivity decline detected since the start-up in 1991 was a clear evidence of the skin damage magnitude, in fact, the fields have not plateau history. The initial high oil and gas rates production added to strong geological structures in which a variety of fluids have been producing (critical volatile and gas condensate) have contributed to the development of a very complex damage scenario; main damage factors identified at early stage of production were fines migration and mineral scales (calcite, siderite, barite, celestite and iron compounds). Research regarding acid stimulation and mineral scale inhibition was the first step trying to mitigate the high oil rate decline. New damage mechanisms were detected as long as the fields were in production, water and condensate blockage, organic scales (wax and asphaltenes), iron sulfide scales, and wettablity changes were the main damage mechanisms detected. Engineering work, laboratory and geological studies, backflow analysis, third parties investigation and an extensive field trial program have been developed to determine the best stimulation program that should be applied in each one of producer/injector wells. Although high success removing formation damage has been obtained, it has been necessary to focus additional effort to find and test new technology addressed to increase both IIOR and stimulation lifetime. Introduction Cusiana and Cupiagua fields constitute the SDLA association contract and are located in Colombian foothills - Colombia, South America. Mirador, Barco and Guadalupe are the producing formations with average properties summarized in tables 1 and 2. The recovery mechanism consists mainly of pressure sustainment and liquids vaporization through gas re-injection; water injection has been implemented for Barco formation in some areas of Cusiana field. As shown in fig 1, the formations in SDLA fields are unique in their porosity - permeability trends. These formations are characterized by very low porosities coupled with reasonable permeabilites. The low porosity of the formations means that the reservoirs have small pore throats that are very susceptible to damage by blockage (both fluid and particulate). This paper is divided into two sections, first we briefly described how the main damage issues has been addressed historically; second, field cases are presented to illustrate the formulation and results of recent strategies aimed on damage control. Complementary information has been included in the annex section presenting a well ranking exercise that qualitatively estimates the degree of damage related to several mechanisms. Approach to Formation Damage Remediation - Past and Present The following section summarizes how the stimulation strategy has been revisited through a detailed review of the primary data on formation damage, stimulation treatments and ongoing technology developments aimed at both improving and understanding the stimulation process; the stimulation with the highest level of impact will be described. Completion Damage. Most of SDLA wells are 5' or 7' monobore type; invert emulsion mud (water in oil 20:80) plus calcium carbonate as weighting material is used for drilling while keeping overbalance pressures 1500 psi average. Cemented liner is set across producing intervals followed by underbalance perforating (2000 - 2600 psi UB, high penetration charges). In general, the extent of completion damage is variable depending on the presence of natural fractures and stability issues which can promote massive mud losses; normally, a varsol + HCl type fluid was used for mud cake dissolution, even though, fines destabilization problems took place in sensitive formations (Barco & Guadalupe) and fluid blockage (mud filtrate and cement filtrate) had not been treated effectively. Currently, mitigation of completion damage is based on prevention and suitable contingency stimulation fluids; for the first, optimal mud particle size / pore size relationships has been achieved which has limited filtrate volumes through a very low K cake; on the other hand, diesel + alcohol followed by EDTA is being applied as stimulation contingency; mud´s calcium carbonate dissolution is being achieved without any collateral problems and fluid and emulsion blockages (caused by mud & cement filtrate) are being directly treated.
- Energy > Oil & Gas > Upstream (1.00)
- Materials > Chemicals > Commodity Chemicals > Petrochemicals (0.47)
- Water & Waste Management > Water Management > Constituents > Salts/Sulphates/Scales (0.34)
- South America > Colombia > Mirador Formation (0.99)
- South America > Colombia > Guadalupe Formation (0.99)
- South America > Colombia > Casanare Department > Llanos Basin > Cusiana Field > Mirador Formation (0.99)
- (2 more...)