Choked Flow in HVO Recovery: Injection and Production in Horizontal Wells

Abstract

The problem of multiphase flows in chokes presents an interesting problem for steam injection and hydrocarbon production. In both cases it is important to evaluate the maximum possible mass fluxes through a perforation. Several models are used in the oil industry for this purpose, e.g., Ashford (1974) [1], Sachdeva et al. (1984) [2], and Perkins (1993) [3]. This paper explains physical principles behind these theories, and outlines their range of applicability. The task of the study is to choose a model that would provide the most general and accurate description of a multiphase flow that can be used for implementation in a reservoir simulator. It is concluded, that existing models are very restricted. They are applicable to particular cases, where the phase transition between the liquid and gas phases is absent. A rigorous description of a multiphase flow with a phase transition does not seem feasible. The possibility of a phase transition introduces a large uncertainty in the flow parameters. This uncertainty essentially exceeds differences between predictions of existing approaches. For this reason, it is sufficiently to analyze flows within the framework of the simplest theory. Such a theory is presented in this report. We derive simple relations to estimate critical flow parameters and transported fluxes. These relations provide a relatively simple evaluation of steam injection and hydrocarbon production without significant loss of accuracy. Preliminary simulation results to illustrate the flow of a wet steam (i.e., two-phase fluid) through the choke are also discussed. Introduction In most heavy oil recovery scheme's, steam is injected into the reservoir to lower the viscosity of the oil, thereby increasing its productivity. Key is the distribution of steam in the reservoir and its optimal use to mobilize as much oil as possible (high Oil-Steam ratios). Efficient steam distribution control in standard completions passing through the multi-sand (i.e., high permeability contrast) reservoir is extremely difficult. Higher-permeability sands usually act as a thief zones with respect to the tighter sands open in the same wellbore. This results in poor injection profile due to the appearance of preferential steam paths. Consequently, many sands cannot be effectively steamed and produced. In order to provide and to control the uniform steam flow distribution from the wellbore to the reservoir, the steam flow rate should depend not on the downstream (reservoir) but on upstream pressure alone. This condition is satisfied if the flow rate through a perforation reaches its maximum value (i.e., steam velocity equals the sonic velocity), which is the critical flow condition. This means that, providing the flow is critical, as long as the pressure in the wellbore is uniform and diameters of the perforations along the well are constant, the steam flow from the wellbore to the reservoir is uniform. Thus, no portion of the reservoir can behave as a thief zone. Limited entry perforations (LEPs) are a completion technology that is used to improve steam injection uniformity along the length of the well [4]. This technique originates from the "pin-point" method, which was commonly utilized in the late 60's as the well completion technique used for hydraulic fracturing [5, 6]. The marked improvement in steam profile control led to the extensive application of LEP technique as injection completion scheme in HVO recovery process. Therefore, description of sub-critical and critical flows, and calculation of maximal allowed flow rates present essential interest for oil industry. Knowledge of these flows is necessary for a proper planning of oil production as well as of (wet) steam and water injection. This paper presents an assessment of the existing multiphase flow theories and derives simple relationships to estimate critical flow parameters and transported fluxes without significant loss of accuracy. It also presents preliminary simulation results of the flow of a wet steam through the LEP perforation.

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“…A literature search for papers pertaining to multiphase flow through wellhead chokes revealed that multiple researchers have developed empirically and theoretically derived correlations for the prediction of multiphase flow through wellhead chokes. The empirical correlation that appeared to be the most directly applicable was developed by Gilbert (1954) for critical multiphase flow through a wellhead choke, which takes the following form (Poettmann and Beck 1963;Omana et al 1969;Fortunati 1972;Ashford 1974;Ashford and Pierce 1975;Sachdeva et al 1986;Ajienka and Ikoku 1987;Al-Attar and Abdul-Majeed 1988;Surbey et al 1988Surbey et al , 1989Ghassan and Maha 1991;Osman and Dhokla 1992;Perkins 1993;Ajienka et al 1994;Al-Towailib and Al-Marhoun 1994;Elgibaly and Nashawi 1998;Guo et al 2002Guo et al , 2007Burstev et al 2006;Schuller et al 2003Schuller et al , 2006Alsafran and Kelkar 2007;Ghareeb and Shedid 2007;Al-Attar 2008, 2010Nasriani and Kalantariasl 2011):…”