Geochemical fingerprinting of hydraulic fracturing fluids from Qusaiba Hot Shale and formation water from Paleozoic petroleum systems, Saudi Arabia

Abstract

Provenance studies of produced water are essential to trace flow dynamics and reservoir compartmentalization in petroleum systems and to quantify fluid recovery rates from unconventional fracturing. Produced water from a hydraulically fractured well in the Qusaiba Hot Shale in the Northern Exploration Area, Saudi Arabia, was daily monitored and analyzed for water chemistry, and environmental (δ2H, δ13C, δ18OH2O, δ18OSO4, δ34SSO4, δ37Cl, 87Sr/86Sr) and cosmogenic isotopes (3H, 14C, 36Cl), to differentiate from reference fluids of supply water, fracturing fluids, and formation water from adjacent Paleozoic units. Initially, recovered water is composed of fracturing fluids and subsequently replaced by a homogeneous cut of pristine formation water. Formation water is composed of dominant meteoric water (approximately 84 vol%) and minor fossil evaporated seawater. The young 14C‐apparent age between 6000 and 6700 years BP and depleted δ18O/δ2H values for the meteoric component confirm the infiltration of surface water into the Qusaiba Hot Shale interval or adjacent units during the Early Holocene Pluvial Period under cooler and wetter climatic conditions than present, which suggest the presence of a very recent, dynamic hydraulic flow system. 36Cl/Cl ratios between 102 × 10−15 and 31 × 10−15 are ambiguous and can be attributed to atmospheric recharge close to the coast, mixing of 36Cl‐enriched Quaternary meteoric recharge with 36Cl‐depleted fossil seawater, and/or hypogene production by U‐Th‐enriched host rock. Produced waters from Qusaiba Hot Shale are within the compositional range of Na‐Cl‐type formation water from Paleozoic reservoir units in northern Saudi Arabia with salinities from 30 000 to 130 000 mg l−1. As a novel technological approach for exploration wells in Northern Saudi Arabia, multi‐isotopic methods were successfully implemented to quantify flowback volumes from hydraulic fracturing, and to fingerprint pristine formation water or pore water in Paleozoic systems on their provenance, residence time, migration pathways, and secondary alteration processes.

Recovery rates of fracturing fluids and provenance of produced water from hydraulic fracturing of Silurian Qusaiba hot shale, northern Saudi Arabia, with implications on fracture network

“…Additionally, it suggests the dominant cut of in situ pore water without the presence of hydraulic communication toward potentially overlying groundwater systems. Additional results from 87 Sr/ 86 Sr and 37 Cl isotope techniques suggest the presence of mixing trends and the differentiation of water types within the recovered postfracturing water from well A (Birkle, 2016).…”

“…Analytical descriptions and interpretations of additional environmental isotopes (d 13 C, d 18 O SO4 , d 34 S SO4 , d 37 Cl, and 87 Sr/ 86 Sr) and radiometric age dating techniques ( 3 H, 14 C, and 36 Cl) on selected samples are described in Birkle (2016).…”

“…• KCl brine (postfracturing): The 5% KCl brine used during the postfracturing cleanout of proppant by coiled tubing consisted of 27,000 and 24,500 mg/L of K and Cl, respectively. • Formation water: Formation water in Saudi Arabian Paleozoic sandstones is generally characterized by NaCl water types with salinities ranging between 35,000 and 129,000 mg/L, as shown for formation water from Jubah, Sarah, Quwarah, Raan, and Khafah reservoirs (Birkle, 2016).…”

“…Average salinities of 46,000 to 50,000 mg/L for pore water from the QHS can be reconstructed by mixing approximately 86% of a dominantly meteoric water component (assuming TDS of 1000 mg/L), with a minor contribution of 14% of evaporated fossil seawater (Birkle, 2016). Age dating with the 14 C radiocarbon method resulted in an apparent early Holocene residence time (6-6.7 ka) for the meteoric component of QHS pore water and a late Pleistocene age (24.8 -0.13 ka to 35.4 -0.18 ka) for analyzed supply water from the Jilh Formation.…”

Origin and Geochemical Evolution of Formation Water in the Dameigou Shale Gas Reservoir in Northern Qaidam Basin

“…The ratio of Cl versus Br is an ideal parameter for identifying the origin of solutes, mixing and dilution of brines, and various water-rock interactions without diagenetic alterations [24]. The Cl/Br molar ratio (1183.43) and Cl concentration (164.62 mM) of formation water is lower than that of salt lakes, respectively, (3082.65-28427.89, 2121.97-5336.90 mM) in the northern Qaidam Basin, including Qinghai Lake [23] (Fig.…”