Determination of the Zone of Maximum Probability of Asphaltenes Precipitation Utilising Experimental Data in an Iranian Carbonate Reservoir

Abstract

Asphaltenes precipitation is one of the major operational problems affecting oil production in the Bangestan reservoir in south of Iranian fields. Precipitation of asphaltenes in reservoirs, wells and production facilities can have severe detrimental impact on the economics of oil production because of a reduction of well productivity and/ or clogging of production facilities. A field methodology based in the influence of pressure in asphaltenes precipitation has been designed and implemented to estimate the zone of maximum probability of asphaltenes precipitation. Nodal analysis is applied to determine pressure versus depth behavior at the well for different operational conditions. Knowing the saturation pressure and the flocculation onset pressure, the methodology allows the determination of the most probable range of depth at which asphaltenes precipitation will occur. The purpose of this methodology is determine the optimum operational conditions that maximize production at minimum risk of asphaltenes precipitation, as well as to select the better preventive measure for each particular case, thus maintaining overall control of the asphaltenes plugging problem. In this paper, field applications of the methodology are shown. Depending on the depth range of asphaltenes precipitation occurrence, reperforation of the producing interval, hydraulic fracture is recommended. Introduction Generally, it is accepted that crude oil is considered as a colloidal system constituted of saturates, asphaltenes, resins and aromatics fraction. Asphaltenes fractions defined as the dispersed colloids in the oil phase and stabilized to some extent by the resins molecules, which act as protective bodies for asphaltene particles. Colloidal asphaltene can be naturally or artificially precipitated if the resins protective shields are removed from asphaltene particle surfaces. The details of asphaltene characterization have been reported in numerous references. In the Iranian Bangestan reservoir it has been observed that asphaltene deposition problems in oil wellbore have increase in past years. This may be due to the changes in reservoir pressure with time and increasing in gas/oil ratio. The later have shown to be an important factor in asphaltene particles flocculation in production systems. This phenomenon decreases reservoir productivity and could increase production costs by requiring frequent chemical treatments for removal of asphaltene deposits. In South Iranian Bangestan carbonate reservoirs, asphaltene precipitated within the well tubing have increasing in deep wells. This paper will focus on monitoring asphaltene flocculation and precipitated in oil well tubing. The monitoring technique to estimate the zone of maximum probability of asphaltene precipitation occurrence is based on the interpretation of the well flowing pressure data obtained from gage ring data collected. Detailed Characterization of the reservoir fluids The first step, to determine the possibility of asphaltene precipitation, is to execute a detailed characterization of the reservoir fluids to know the composition of the oil and to define the parameters (Table 1) that promote the asphaltene precipitation. Using simple screening rules in Iranian Bangestan reservoirs: asphaltene problems can be expected with light crude that are high in C1-C3 content (more than 50 vol%) and relatively low C7+ content, with high bubble point pressure(Bp) and a large difference between reservoir pressure (Pr) and bubble point pressure with a high oil compressibility(Coi more than 16E-6 1/psi). Among those parameter are: the proportion of each fraction of the crude oil, this is, the percentages of saturated hydrocarbons, aromatic hydrocarbons, resins and asphaltenes presented in the crudee oil table 2 represents the result obtained by SARA test which oils with high content of saturated hydrocarbons, few resins will have greater probability of asphaltene precipitation.

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

“…Asphaltene problems have been treated mechanically, chemically, and/or operationally. Among available remedies in each technology that have been widely applied in the world (Jamaluddin et al 1996;Avila et al 2001;Kokal et al 2003;Wang and Civan 2005;Hamid 2006;Al-Ghazi and Lawson 2007;Frost et al 2008), the most conventional ways have been applied in our target fi eld. The selection of remedial action was based on operational and cost reasons.…”

Estimation of the SARA Composition of Crude Oils from Bubblepoint Pressure Data

“…Figures – show respectively the aromatic SARA compositions versus the saturate SARA compositions; the resin SARA compositions versus the saturate SARA compositions; the asphaltene SARA compositions versus the saturate SARA compositions, and the aromatic SARA compositions versus resin SARA compositions. In all cases, the data were taken from our database, − …”

“…In this work, we would rather use one W for each oil type (bitumen/heavy-oil/medium-oil/light-oil). For the set of 341 crude oil compositions studied in this work, − …”

“…The probability density W , for an oil, was estimated by the histogram of SARA compositions taken from the data set. − As occur in all histograms in statistics, if the mesh size is big enough, it ...…”

“…Table shows some features of our database. The set includes SARA analyses reported in 108 public papers found in open and private literature. ,− …”