Proppant Fracture for Unconventional Carbonate Source Rock in Saudi Arabia
Authors: Carpenter Chris 
Published: June 2016

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper IPTC 17765, “First Successful Proppant Fracture for Unconventional Carbonate Source Rock in Saudi Arabia,” by Nayef Ibrahim Al-Mulhim, SPE, Ali Hussein Al-Saihati, SPE, Ahmed M. Hakami, SPE, Moataz Al-Harbi, SPE, and Khalid Saeed Asiri, SPE, Saudi Aramco, prepared for the 2014 International Petroleum Technology Conference, Kuala Lumpur, 10–12 December. The paper has not been peer reviewed.

A type of unconventional play currently being evaluated is a carbonate source rock with nanodarcy permeability and very low porosity. This paper will discuss the hydraulic-fracturing- stimulation design, execution, and evaluation for the first successful proppant-fracturing treatment in an unconventional carbonate source rock in Saudi Arabia. The successful two-stage treatment proved that proppant-fracturing techniques could be used to stimulate carbonate formations after modifying the stimulation design (specifically, the perforation strategy, fracturing fluids, and proppant type).

Introduction

The operator has embarked on an exploration-and-appraisal project to assess unconventional-resource potential in three geographic areas: northwest, South Ghawar, and East Ghawar. Hydraulic-fracturing techniques will be used to enhance production by connecting natural fissures and creating high-connectivity pathways through which gas can flow into the well. The initial focus is in the northwest and in the area of Ghawar. Initial knowledge building from similar plays in North America is being supplemented with internal technical studies and research programs to help solve geological and engineering challenges unique to Saudi Arabia and to locate specific wells planned for 2014.

Acid vs. Proppant Fracturing

The operator has used mainly acid fracturing and matrix acidizing to increase production rates from carbonate formations in conventional gas fields, while proppant fracturing was used predominantly in sandstone formations. This methodology, coupled with the fact that all previous attempts to stimulate carbonate formations in Saudi Arabia resulted in premature screenouts after only 10% of the proppant had been placed in the formation, clearly demonstrates the significance of the first successful proppant-fracturing treatment in an unconventional carbonate source rock in Saudi Arabia.

Jafurah Basin Source Rocks

The Jurassic sediments being targeted in the Jafurah basin as unconventional reservoirs are carbonate source rocks within the Tuwaiq Mountain, Hanifa, and locally basal Jubaila formations (please see the complete paper for a detailed geological description). The H-1 well is the first well drilled on a seismic anomaly, and it encountered a thick organicrich Jurassic source rock. The thick sequence of source rock in the H-1 well, as well as other areas within the basin, may suggest the possibility of a commercially viable unconventional play. As a followup to the drilling of the H-1 well, a geophysical forward-modeling project was initiated to investigate the cause of the seismic-amplitude anomaly in the Jafurah basin. The study revealed that the formation encountered in the H-1 well has an overall lower acoustic impedance, which appears to be the result of its high total organic content.

Drilling and Coring

The H-2 well, east of the giant Ghawar field, was drilled to evaluate several Jurassic source-rock targets. The well was completed with 4½-in. tubing, a 7-in. liner with a 7-in. permanent packer, and a 25-ft sealbore receptacle. The tubing and annulus were displaced with 65-lbm/ft3 brine. The well was designed to be re-entered for horizontal sidetracking.

Five cores were cut for laboratory testing and analysis. Acid-solubility tests were performed on the core-plug samples to determine their solubility in hydrochloric acid (HCl). X-ray-diffraction analysis was performed on four core samples before and after the acid-solubility tests, showing that the four samples analyzed consisted mainly of calcite with smaller fractions of dolomite, quartz, anhydrite, pyrite, and clays.

Perforation-Design Strategy

Deep-penetrating charges were used in Well H-2, in conjunction with underbalanced perforating to minimize perforation damage and ensure clean perforations. In addition, 3,000 gal of 15% HCl was pumped as a preflush before pumping the pad in each stimulation treatment to further aid in removal of debris from the perforation tunnels.