Asphaltene Precipitation in a Saturated Gas-Cap Reservoir

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractAsphaltene deposits were obtained from three high gas/oil ratio (GOR) wells in an offshore field in the Arabian Gulf. The reservoir is saturated and there is a gas-cap present in the field. In many wells the gas cones into the producing wells and causes precipitation of asphaltenes from the crude by stripping. These asphaltenes deposit in the wellbore and have the potential to create plugging problems.This paper describes the results of an investigative study that was initiated to determine the precipitation mechanism and ways to alleviate the deposition problem. Asphaltene precipitation experiments were conducted at reservoir conditions in a special pressure-volume-temperature (PVT) apparatus. The effect of GOR on asphaltene precipitation was determined by titrating the reservoir oil with gas-cap gas. Bulk deposition tests were also performed at different GORs with reservoir fluids. The results demonstrate that the onset of asphaltene precipitation occurs at relatively low GOR values. The amount of asphaltene precipitated at the onset is small. Asphaltene precipitation and deposition increase with increasing GORs. Asphaltene deposition envelopes are provided for the reservoir oil as a function of pressure and temperature. Recommendations were made to alleviate the problem by controlling the maximum producing GORs to less than 1000 scf/stb. Recipes for solvent treatment including asphaltene dispersants are also described in the paper and are currently being considered for implementation in the field.

Ready for Gas Injection: Asphaltene Risk Evaluation by Mathematical Modeling of Asphaltene-Precipitation Envelope (APE) With Integration of All Laboratory Deliverables

“…The increase of asphaltene risks through gas injection has been recognized as a general rule (Kokal et al 2003;Srivastava et al 1999;Parra-Ramirez et al 2001;Sarma 2003;Jamaluddin et al 2000;Kokal et al 2004;Negahban et al 2005;Okwen 2006; Moghadasi et al 2006). A preparatory evaluation of asphaltene behavior under gas-mixing conditions is important to minimize risks and to optimize the gas-injection project.…”

Compositional Dependence of Wetting and Contact Angles in Solid-Liquid-Liquid Systems under Realistic Environments

“…This situation was clearly depicted in Figure 1, where the asphaltenes were slowly migrating towards the needle with time due to gravity and then finally depositing on the needle. The addition of injection gas to the reservoir crude oil during the conventional CO 2 gas injection displacement processes in the field has also demonstrated asphaltene precipitation from crude oil and subsequent alteration of reservoir wettabilities towards more strongly oil-wet (Kokal et al, 2004;Wang et al, 2004). The added light gaseous components would change the original composition of crude oil and hence make the oil unstable.…”

“…The added light gaseous components would change the original composition of crude oil and hence make the oil unstable. However, on the other hand, the depressurization during production in crude oil reservoirs has also resulted in more oil-wet characteristics for the reservoir due to the release of light gaseous ends dissolved in the crude oil (Kokal et al, 2004;Wang et al, 2004). Thus, it appears that both the addition as well as removal of light gaseous ends from the crude oil would cause wettability alterations towards more strongly oil-wet behaviour.…”

Contribution from Laboratory to Field: Case Studies of Asphaltene Precipitation Risk Evaluation

“…As a result of this increasing CO 2 supply estimation, the growth of CO 2 EOR oil production is predicted to be sustainable during the period from 2012 to 2018, as shown in Figure . The increase in asphaltene risks by gas injection has been widely recognized. − It is therefore expected that future requirements to evaluate asphaltene flow assurance for gas injection projects will increase.…”