Al-Garadi, Karem (King Fahd University of Petroleum and Minerals) | Aldughaither, Abdulaziz (King Fahd University of Petroleum and Minerals) | Ba alawi, Mustafa (King Fahd University of Petroleum and Minerals) | Al-Hashim, Hasan (King Fahd University of Petroleum and Minerals) | Sibaweihi, Najmudeen (King Fahd University of Petroleum and Minerals) | Said, Mohamed (King Fahd University of Petroleum and Minerals)
Condensate banking has been identified to cause significant drop in gas relative permeability and consequently reduction of the productivity of gas condensate wells. To overcome this problem, hydraulic fracturing has been used as a mean to minimize or eliminate this phenomenon. Furthermore multistage hydraulic fracturing techniques have been used to enhance the productivity of horizontal gas condensate wells especially in low permeability formation. Even though multistage hydraulic fracturing has provided an effective solution for condensate blockage to some extent as it promotes linear flow modes which will minimize the pressure drops and consequently improves the inflow performance considerably. However, this technique is very costly, and has to be optimized to get the best long-term performance of the multistage fractured horizontal gas condensate wells.
In this paper, multiple sensitivity analyses were conducted in order to come up with an optimum multistage hydraulic fracturing scenario. In these analyses, our manipulations were focused mainly on the operational parameters such as fractures half length, fractures conductivity using compositional commercial simulator. CMG-GEM simulator was used to investigate the different cases proposed for applying multistage hydraulic fracturing of horizontal gas condensate wells. The investigation began with a base case scenario where the fractures half-length were fixed for all stages with equal spacing between them. Then, six more fractures half-length patterns were created by introducing new approach where the well performance was studied if they are in increasing trend away from the wellbore (coning-up), or in a decreasing trend (coning-down). Well performance is furtherly addressed when the fractures half-length arrangements formed parabolic shapes including both occasions of concaving upward and downward. Finally, the last two patterns illustrated the effect of having the fractures half-length arrangements both skewed to the left and right on well productivity.
The investigation of the effect of changing the multistage hydraulic fractures half-length distribution patterns on the performance of a gas condensate well was conducted and resulted in parabolic up distribution pattern to be the optimum pattern amongst the other tested ones. It results in the highest cumulative both gas and condensate production. It also maintains the gas flow rate and bottom hole pressure more efficiently. The parabolic up distribution pattern confirms that the majority of gas production was fed by the fractures at the heel and at the toe of the horizontal drainhole which is in agreement with the flux distribution along the horizontal well.
Eliebid, Mohammed (King Fahd University of Petroleum and Minerals) | Mahmoud, Mohamed (King Fahd University of Petroleum and Minerals) | Al-Yousef, Hasan Y. (King Fahd University of Petroleum and Minerals) | Elkatatny, Salaheldin (King Fahd University of Petroleum and Minerals) | Al-Garadi, Karem (King Fahd University of Petroleum and Minerals)
Pulse-decay method is a technique used to estimate cores permeability using gas injection based on Darcy's flow model. Helium and nitrogen are generally used when the target formation is an oil formation or liquid permeability is sought. However, new approaches suggest using CH4 to avoid correcting for properties difference between the testing fluid and reservoir fluid. This study focused on the latter approach to quantify the correction to gas adsorption. The Cui et. al, model based on Langmuir adsorption isotherm is modified to Cui-Freundlich isotherm which has been proven adequate to fit the adsorption on intact reservoir rocks. The model is developed using gas and rock properties and the approach is generalized by using reduced pressure and temperature to account for the gas compressibility. The results of the modified model showed that the new model can capture effective porosity of adsorption Φα used to correct the pulse-decay storage capacity parameters a and b. This correction in the storage volume and rock porosity values will enhance the permeability estimation in the ultra-tight rock samples.
Tight rock sample permeability is usually measured in the laboratory using gas. Unsteady-state gas permeability was proposed to avoid the shortcomings of the steady state gas permeability determination. Steady state gas permeability measurements are time consuming when used in very tight rocks because the time required for each steady state measurement.
Bruce et al. (1952) introduced the use of unsteady-state gas permeability method to determine the permeability of tight rocks. Wallick and Aronofsky (1954) introduced the use of pulse decay set-up to measure the tight rocks permeability using the unsteady state gas permeability measurements. The experimental set-up involves monitoring the differential pressure evolution as a function of time across the rock sample. Each face of the rock sample is connected to a tank, upstream and downstream tanks. This set-up was introduced by Aronofsky et al. (1959). The upstream tank pressure is increased gradually by a specific pressure increment. Several modifications were made to enhance the pulse decay measurements and to shorten the experimental time required to measure the tight rock permeability (Jones, 1997). The pressure in the upstream tank (reservoir) should be raised in incremental that is almost 1 to 3% the value of the downstream transducer pressure. The downstream pressure should be stabilized and this might take hours or minutes based on the sample permeability. Then the pressure pulse is applied, this may be different than the initial pressure drop because of the dead volume.