Proving the Concept of Unconventional Gas Reservoirs in Saudi Arabia Through Multistage Fractured Horizontal Wells

Abstract

Saudi Arabia has embarked on an exploration journey for its unconventional gas resources by recently targeting three different areas across the Kingdom. The targeted formations include tight sandstone, shale and tight carbonate with a permeability range of 200 nano-darcy to 0.1 MD. Extensive exploratory work has been performed in each of the areas through drilling vertical wells to identify and characterize potential targets through coring and open-hole logging along with flow potential testing of those targets after placing vertical fractures, which is beyond the scope of this paper. This paper highlights the progress of the unconventional program through drilling horizontal mono-bore wells and stimulating them with multistage fracturing using Plug-N-Perf technique. Three case studies, one from each targeted formations, are presented in this paper. The subjects addressed are: Well completion including the selection of tubing and liner sizes, metallurgy and grades along with performing stress and thermal analysis simulating the expected loads during proppant fracturing to determine the maximum safe loads at each stage. Proppant fracturing design including the number of stages and clusters, the spacing of stages, proppant type, size and volume, and fracturing fluid systems. The design is based upon the geomechanical and petrophysical interpretations of the openhole logs together with onsite calibrations and measurements. Plug-N-Perf and fracture stimulation operations and execution Fracture fluid clean up and flow testing The paper summarizes the workflow adopted, the lessons learned and challenges overcome after drilling, completing, fracturing and flow testing of several unconventional gas wells in Saudi Arabia.

Characterization of carbonate mudrocks of the Jurassic Tuwaiq Mountain Formation, Jafurah basin, Saudi Arabia: Implications for unconventional reservoir potential evaluation

“…The production log analysis showed that all stimulated stages and cluster for the three wells were contributing to the wells production (Al-Momin et al, 2015). It was also determined that stages stimulated by both conventional and channel fracturing stimulation contributed to production.…”

“…Wells were completed with a 4½ inch production liner and 5½ inch tubing. This completion was selected to minimize friction pressure at higher fracturing pump rate (Al-Momin et al, 2015). Different fracturing techniques were tested to investigate operational efficiency, cost and potential to maximize well performance.…”

“…All fracturing treatments started with 6000 gallons of pre-pad acid stage to breakdown the formation, manage near wellbore friction and reduce treating pressure, followed by linear gel and cross-linked gel in the pad and slurry stages (Al-Momin et al, 2015). During the initial stimulation trials, slickwater was found to be prone to high treating pressure and early screenouts.…”

The Effect of Hydraulic Fracture Geometry on Well Productivity in Shale Oil Plays with High Pore Pressure

“…The contribution of the exterior flow to the stimulated reservoir volume is minimal because we only consider the reactivation of natural fractures near the stimulated hydraulic fractures, and the matrix has ultra-low permeability [41]. Based on the reported massive stimulation jobs performed in mudrock plays worldwide [44][45][46][47][48][49], we estimate a total fracturing fluid volume injected into the rock of 12,700 m 3 (∼80,000 bbls) distributed evenly among the 22 stages. We consider the same fracturing fluid volume for all fracture scenarios and predetermine the stimulated volume's geometry based on each scenario.…”

“…Thus, the bubble point pressure is below the reservoir pressure. The shale reservoirs in the U.S. and Saudi Arabia report pore pressure gradients between 0.014 MPa/m and 0.020 MPa/m (∼0.6 psi/ft-0.9 psi/ft) [38,44,46]. Thus, our study considers an overpressured reservoir with a reservoir fluid pressure gradient of 0.0195 MPa/m (∼0.85 psi/ft).…”