Hydraulic fracturing activities in tight gas wells in Saudi Arabia have been exponentially increasing to meet domestic demand for natural gas. During each fracturing stage, up to 125,000 gallons of groundwater is currently being used. The need to reduce groundwater usage during fracturing treatments has been set as a priority, and alternative water sources for fracturing applications that can significantly reduce groundwater usage have been intensively explored. One such alternative water source is seawater as a base fluid for hydraulic fracturing. The primary challenge for this application is the tendency for scale precipitation due to the high sulfate content in seawater and its potential incompatibility with formation water. Without proper prevention and mitigation measures, this scale precipitation can induce formation damage and reduce the fracture conductivity. To minimize scaling tendencies, an in-house multidisciplinary team has performed extensive collaborative research to identify a scale inhibitor appropriate for Arabian Gulf seawater and formation water. Scale precipitation can be further mitigated by filtering the seawater with a nanofiltration system to dramatically reduce the sulfate ion as well as lower the calcium and magnesium ions. The successful application of seawater-based fracturing fluid in Saudi Arabia opens up the door to minimizing consumption of groundwater in hydraulic fracturing operations. Millions of gallons of groundwater could be saved and development of sustainable water resources could be achieved. This paper will describe the optimization of a scale inhibitor and fracturing fluid system, the selection of the nanofiltration system, and the first field applications of the seawater based fracturing fluid system in high-temperature gas wells in Saudi Arabia.
Clay swelling, dispersion and migration due to water-sensitive clay minerals in the producing formation can substantially reduce rock and retained proppant permeability resulting in reduced well productivity. The effects of water-based fracturing fluids in water-sensitive formations have been extensively investigated which led to development of different types of clay stabilizers based on type of clays, bottomhole temperature, and clay protection time. The use of KCl or NaCl brine up to concentration of 6% is well known clay stabilizing method for swellable and migratory clays during the stimulation treatment.However, using high salt content brines have some limitations and constrains. The performance of crosslinkers (Borate or Zirconium) and breakers are often affected when using high salt concentration in the base fracturing fluids. The sandstone formations of Saudi Arabia have been reported to be "water-sensitive" and can be easily damaged by fresh water. A novel clay stabilization liquid additive has been successfully introduced as a substitute to inorganic salts in fracturing fluids for sandstone formation in Saudi Arabia. This new permanent clay control additive is cationic polymer with ultra-low molecular weight (PC-4) and compatible with borate and zirconium crosslinkers. It also reduces safety concerns and operational time by eliminating handling and mixing of huge amount of salts on location.This paper provides details on lab testing, and field implementation of the novel cost effective clay control additive in HTHP sandstone gas well during proppant fracture treatment.
Production logging in horizontal wells presents particular challenges, especially when they are completed uncemented using prepacked screens or slotted liners. These challenges are attributed to well geometry, i.e., the existence of severe doglegs and undulations, where trapped fluids that could directly affect and influence data readings from the tools, such as stagnant water, may lie either inside or outside the liner in low areas at the bottom of the well, or stagnant gas that may accumulate on the high side of drain-hole undulations.Considering the challenges mentioned above, an integrated horizontal multiphase production logging tool (IHMPLT) is usually required, and in many cases this tool needs to be complimented with a pulsed neutron logging tool (PNLT) to have a more accurate reading of fluid entries.Over the last 20-years, coiled tubing (CT) equipped with electric cable has been widely used to conduct production logging in horizontal wells, and more recently, CT equipped with an optical fiber has eliminated the restrictions associated with CT equipped with electric cable while enabling several advantages, such as distributed temperature sensing (DTS) to compliment production profiles from IHMPLT. The previous system was unable to run PNLT. To tackle the above described limitations, and having a more robust portfolio of production logging available, a new solution of real-time downhole measurements via CT equipped with fiber optics has been introduced to enable real-time data acquisition of DTS, IHMPLT, and PNLT logs.This paper discusses the case history of this first worldwide application. It also provides lessons learned and perspectives for this technology.
Saudi Aramco has been using coiled tubing (CT) to acid stimulate gas wells completed as single or multiple open hole horizontal laterals in carbonate reservoirs. These CT interventions have evolved from pumping the treatment fluids through normal nozzles, to high-pressure jetting with or without a simultaneous bullheading of inert fluid through CT tubing annulus. Until recently, there was no CT bottom-hole assembly (BHA) available on the market to provide realtime downhole data monitoring during CT acid stimulation. Therefore, these types of stimulation jobs followed a predetermined pumping schedule, assuming that fluids are squeezed at the nozzles depth while reciprocating the CT string from toe to heel. The operator had no means to control the acid coverage across the extended reach open hole laterals.The bottom-hole pressure (BHP) inside and outside the CT string, monitored real-time with the fiber optic bottom-hole assembly (FOBHA) allows the operator to adjust the differential pressure across the high-pressure jetting tool nozzles. The distributed temperature survey (DTS) recorded with the fiber optic at key stages of the treatment helps identify initial thief zones and any further developing ones during the acid stimulation treatment. Tracking with a DTS, the fluids placement through the high-pressure jetting tool showed that acid was still being injected into thief zones and not squeezed at the nozzles depth. DTS is therefore used to adjust the real-time pumping schedule by deciding when, where, what type and what quantity of diverter to pump to get uniform acid placement across target intervals.The ability to place stimulation fluids in a highly effective way is the most important element in any successful production enhancement stimulation job. This paper will detail case histories of gas producers in which a fiber optic enabled coiled tubing (FOECT) and a FOBHA were successfully run together to record real-time downhole data in an effort to assess the full stimulation effect of an acid matrix stimulation treatment, and to control and optimize the CT operation.Several cases demonstrating the effectiveness of the FOECT matrix stimulation technique are highlighted in this paper.
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