Management of Asphaltenes Deposition in a Giant Carbonate Onshore Oil Field, Abu Dhabi, U.A.E.

Abstract

Recently observed production behavior in a maturing carbonate oil reservoir indicated that many production strings were getting plugged with solid scales, requiring tubing clean-out jobs. This is the main reservoir of a supergiant onshore carbonate oil field operated by ADCO since 1973. Some cases proved to be no more than calcium carbonate scaling following water breakthrough and the tubing blockage was successfully treated with acid washing. A number of plugged strings revealed that a non-mineral hard scale was the cause of the blockage. Upon analysis, such scales proved to have an organic composition rich in asphaltenes. While solvent washing was successful in removing the blockage, rapid reoccurrence was observed in many cases. The subsurface asset team embarked on a detailed reservoir monitoring and fluid compatibility study to establish causative factors. One of the aims of the study was to check a possible link between the asphaltenes deposition with a naturally occurring tarmat and a rich-gas injection pilot, both located in the severely affected part of the reservoir. This work revealed that although the severity of the problem is higher in the tarmat area, asphaltenes mobilization from the tarmat layer was not considered a realistic mechanism. Although PVT studies revealed that rich gas dissolution in the crude at reservoir conditions triggered asphaltenes instability and precipitation but occurrence of asphaltenes deposition in the field seemed unrelated to the rich-gas injection as the injected gas was moving in a different reservoir subzone. Most of the plugged strings were unlikely to have had gas breakthrough at the time of problem detection and no clear spatial relationship could be evidenced. A preferred explanation may be that asphaltenes precipitation is related to differences in crude oil composition within the studied reservoir. The reservoir might have seen successive oil influxes from two source rocks with wide distribution of mixing ratios. Asphaltenes originating from one of the source rocks might cause greater fluid instability even at the observed low concentrations. Production rate sensitivities indicated that asphaltenes blockage was retarded at higher production rates. Many asphaltenes dispersant/inhibitor chemicals were evaluated for effective tubing clean-out and preventing asphaltenes deposition. Some chemicals proved to be more effective in mitigation and prevention of asphaltenes deposition.

Determination of Asphaltene Stability in Crude Oils Using a Deposit Level Test Coupled with a Spot Test: A Simple and Qualitative Approach

“…Deposition is the consequence of the aggregation of asphaltene particles to a size which can settle down. The aggregation process might be governed by factors such as crude oil SARA composition and asphaltene composition and properties like polarity, dielectric constant, etc. ,− On the other hand, the amount of asphaltene deposition might depend upon the overall asphaltene weight percent in the crude oil in the dissolved phase. An oil sample having a higher potential of generating asphaltene deposits at faster rates is more risky than an oil sample that produced a lower amount of asphaltene at slower rates.…”

“…It was also reported that asphaltenes collected from the field are more polar than asphaltene extracted from the same crude under laboratory conditions . Lastly, the geological settings, presence of tar mat, and biomarker correlation of the crude oil and the source rock also facilitate the determination of asphaltene stability in oils . However, these methods are still not very common or mature and add difficulty to the interpretations of instability and stability from the obtained results.…”

Removal of Plugged Asphaltene in a Reservoir by Earthquakes

“…Fig. 4 shows that the CIIs of both Well A and Well B were comparable or higher than those from other fluids from locations in the Middle East (Kokal 2003;Misra et al 2011;Kabir and Jamauddin 2002;Al-Qattan et al 2012) and Venezuela (Garcia et al 2001) that have experienced asphaltene problems in their production systems.…”

Effects of hydrophobic CaO and SiO2 nanoparticles on Asphaltene Precipitation Envelope (APE): an experimental and modeling approach

“…It was observed that the asphaltene precipitation decreased at a high ratio of resin to asphaltene, and the resin polar head coated asphaltene molecules and the nonpolar parts interacted directly with oil [17]. Asphaltenes stability was analyzed by many methods including: the Colloidal Instability Index (CII) [18,19], De Boer's diagram [20], Refractive index [3] and hydrogen to carbon ratio [21]. Asphaltenes Precipitation Envelopes (APE), gravimetric, acoustic resonance, nearinfrared light scattering and filtration were the most common methods for detecting the severity of asphaltenes [20].…”

“…Asphaltenes stability was analyzed by many methods including: the Colloidal Instability Index (CII) [18,19], De Boer's diagram [20], Refractive index [3] and hydrogen to carbon ratio [21]. Asphaltenes Precipitation Envelopes (APE), gravimetric, acoustic resonance, nearinfrared light scattering and filtration were the most common methods for detecting the severity of asphaltenes [20]. Akbarzadeh et al [22] performed a study on the flow assurance problem due to asphaltene precipitation.…”