RIASSUNTO
Abstract
The deposition and accumulation of inorganic scales is a major concern for oil and gas producing companies worldwide. This concern typically stems from two main factors: the strong possibility of total production loss due to scale plugging of production conduits, and the significant impact that managing scaling challenges could have on field economics. These issues become even more pronounced for marginal and mature field developments.
Following the retrieval of scale deposits (predominantly calcite and halite) in a number of wells in a mature gas field in eastern Europe, implementing an effective scale-management strategy became top priority. This paper discusses the principal components of scale-management strategy formulation, including the procedures adopted to explicitly identify, assess, and rank at-risk producer wells in the field. A systematic approach was used to combine the main aspects of scale management, ranging from thermodynamic predictions of scale deposition to a scaling risk assessment. Additionally, the approach was adapted to address the significant degree of uncertainty emanating from the water chemistry and pressure/temperature history, eventually enabling the identification and proposal of adequate mitigation plans with attendant potential for optimization of field production.
Workflows developed on this field are described, including field results as examples. Our work helped to create a risk matrix and well ranking based on saturation ratio. It helped to characterize the location of the precipitating scale. Finally, we highlight the different remediation techniques that have been proposed and their success rate based on the recommendations following their field implementation three years later.
Introduction
The Laslau Mare field is located in the central part of the Transylvanian basin, 25 mi [40 km] northeast of Medias in Romania. The field started producing in the 1970s, and its total gas field production peaked in 1980. This period was followed by extensive decline until 2003, when the Schlumberger field rehabilitation agreement with Romgaz began. At present, the field has 53 active wells.
During certain workover and sand-bailer operations (mostly in 2009), both calcite and halite scale deposits were found in around 10 of the wells in the Laslau Mare field. As a result, it is believed that most wells in the field may have been subjected to varying degrees of formation damage due to accumulation of scale over time, which could have significantly impacted production. Therefore, it was understood that while removing scale deposits could increase current production, incremental production could be sustained by defining a cost-effective scale-management strategy.
This paper describes how diagnostic predictions of scaling tendencies were conducted in the Laslau Mare field and how the predictions allowed identification and selection of appropriate mitigation and remediation techniques. These techniques facilitated informed discussions geared towards implementing a cost-effective scale-management strategy. Reflecting on the risk matrix developed during the evaluation study, results from field application of recommended scale management techniques are discussed after three years of production.