An Improved Correlation to Estimate Productivity Index in Horizontal Wells

Abstract

Proposal Because their great efficiency in producing higher flow rates per unit pressure drawdown, horizontal wells have currently become a popular alternative for the development of hydrocarbon fields around the world. So far, most of the introduced correlations to estimate the productivity index for these wells have shown certain differences among their results. This does not allow us to properly establish which one of them provides the closest value to the actual one, since there is no evidence of a trustable enough reference point. Throughout the years, several investigations for the determination of horizontal-well productivity index have been carried out. These researches have been focused on the determination of steady-state solutions for the above-mentioned parameter, therefore, a diverse number of correlations have been introduced. These correlations have been presented by such very well-known researchers as Giger, Borisov3, Merkulov 2, Renard & Dupuy2–5 and Joshi2–5. They are mainly based upon complex analytic solutions which may have some uncertainties when applying them. This paper proposes an improved steady-state correlation to calculate productivity index for horizontal wells and evaluates the most commonly used existing correlations to estimate this parameter by using numerical simulation. Besides that, a sensitivity analysis on the influence of the variation of each variable in the existing and proposed models was carried out. The analysis was conducted by generating a synthetic drawdown test by means of a commercial reservoir simulator. Using the pressure derivative curve, a time range where steady-state behavior takes place was defined. Then, a simulation was performed with the purpose of determining the pressure distribution in the reservoir within that range of time. This allows us to estimate the horizontal-well productivity index for any drainage radius. More than 500 simulation runs were performed to estimate the results obtained by the improved correlation introduced in this work and the existing ones. Several plots of productivity index versus each one of the model variables were constructed for comparison purposes. It was observed that Joshi s correlation matches well with the simulated results. However, the proposed correlation provides much better results than those provided by Joshi's within a very wide range of variation of the parameters involved in the different correlations. Introduction Throughout the years, several investigations on the determination of the productivity index for horizontal wells have been developed. These researches have been focused on finding a steady-state flow solution which has resulted in different correlations. These correlations were developed by such well-known researchers as Giger2, Borisov 3, Merkulov2–5, Renard & Dupuy2–5 and Joshi2–5. However, there are remarkable differences among the results they provide which does not allow us to clearly establish which one matches closely the actual value since not accurate comparison point has been given. In this paper, based on numerical simulation, we define which existing correlation is the most appropriate for the estimation of the productivity index in horizontal wells. The limitation or application range for them is presented, as well. For this purpose, we chose a practical and very useful way to perform our computations: Numerical simulation. Because their popular use in the oil industry around the globe, we combined the power of PEBI grids, Eclipse 300 and Eclipse Office to develop our work. PEBI grids have provided a very convenient way to numerically represent horizontal wells, faults and pinchouts1.

A new and simple model for the prediction of horizontal well productivity in gas condensate reservoirs

“…Over the last few years, since horizontal wells have been drilled more economically, the number of horizontal wells has grown exponentially worldwide. Therefore, many studies have been conducted to propose an accurate formulation for the calculation of the productivity of such wells at steady state (SS) or pseudo steady state (PSS) conditions ( (Borisov, 1964), (Joshi, 1991), (Giger et al, 1984), (Permadi, 1995), (Renard and Dupuy, 1991), (Lu, 2001), (Elgaghah et al, 1996), (Economides et al, 1996), (Furui et al, 2003), (Wang and Eaton, 2007) , (Sheng and J, 2007), (Escobar and Montealegre, 2008) , (Economides et al, 1996), (Helmy and Wattenbarger, 1998), (Lu and Tiab, 2007), (Babu and Odeh, 1989) and (Goode and Kuchuk, 1991)).…”

A New, Accurate and Simple Model For Calculation of Horizontal Well Productivity in Gas and Gas Condensate Reservoirs

“…Over the last few years, since more economical ways of drilling horizontal wells have been found, the number of such wells has grown exponentially worldwide. Many studies have therefore been conducted to propose an accurate formulation for productivity calculation of such wells at steady state (SS) or pseudo steady state (PSS) conditions (Borisov, 1964, Joshi, 1991, Giger et al, 1984, Permadi, 1995, Renard and Dupuy, 1991, Lu, 2001, Elgaghah et al, 1996, Economides et al, 1996, Furui et al, 2003, Wang and Eaton, 2007, Sheng, 2007, Escobar and Montealegre, 2008, Economides et al, 1996, Helmy and Wattenbarger, 1998, Lu and Tiab, 2007, Babu and Odeh, 1989and Goode and Kuchuk, 1991. However, to the best of authors' knowledge, these equations are only applicable for single-phase flow conditions.…”