In permeable carbonate formations, hydrochloric (HCl) acid treatments are usually utilized to remove formation damage and mud filter cake induced by drilling operations. Usually, the practice is to implement these stimulation activities after the rig is released and permanent completion is set. In some cases, these stimulation treatments cannot be performed due to tight project schedules and the need to deliver production/injection targets on time with minimum risk and environmental impact. These unique scheduling issues dictates stimulating the well before landing the production string and while the rig is on-site to save rig time and minimize expenditures. Yet, stimulating the well in this situation will increase its injectivty, which may lead to severe lost circulation problems and potentially serious well control issues. The objective of this paper is to present several field cases designed to achieve effective stimulation treatments while combating the issues of lost circulation. Several stimulation recipes were studied in the lab and deployed in the field trying to address the goals of having a recipe that provide stimulation mechanism with the highest safety commitment and controlled investment. For example, acidic brine with different HCl concentrations, enzymes and organic acids were used. These recipes were applied during the cleanout trips after reaching total depth of the well. Therefore, they were used to displace the drilling mud out of the hole. As the displacement began, immediate lost circulation (100 barrels per hour (bph) to 150 bph) took place, which hindered well safety. Losses were beyond the rig pump capabilities and mandated immediate curing processes with Hydroxyethyl Cellulose (HEC) Polymer pills, which damaged the well again. This paper details the experience gained from stimulating more than 10 wells where acidizing jobs have been performed before running the completion. It discusses efforts and techniques utilized to stimulate these wells but allowing the rig to perform casing clean out, mud displacement, pulling out assembly, and running the completion without encountering losses. Normally, this process takes an average of 3-to-5 days to complete. Subsequently, all tried stimulation recipes caused early lost circulation with varying degrees of severity. Lessons learned from these treatments are studied in this paper. These lessons were beneficial in optimizing and integrating stimulation and drilling activities. These synchronized efforts proved realized cost savings and fast turnover of wells.
A carbonate field in Saudi Arabia is undergoing major development requiring water injection wells to provide peripheral matrix water injection as pressure maintenance scheme to support oil production. The field is characterized by a tar mat zone, which potentially could isolate the oil reservoir from the planned pressure support and serve as a barrier for the water injection. Therefore, the injection wells were geosteered horizontally right above the tar " barrier?? into the transition zone between the heavy and lighter oil, which poses a challenge in assuring adequate pressure support to the producers, without leaving pockets of relatively high oil saturation behind the waterflood front. To address transmissibility uncertainty between producers and the injectors, long-term injection (LTI) pilot tests were designed utilizing one water injector and six observation wells to capture pressure signals. Building the surface facility to deliver the required test as planned was challenging, starting with the seawater as a source, to water treatment and ending with pump selection. This paper discusses the unique layout of the LTI surface equipment, a mini-plant by itself, and how operational challenges were overcome in the field. The authors highlight some operational issues related to the LTI test that had almost 90% efficiency from operating over 200 days and over 2 million barrels of injected filtered and treated seawater volume, as well as present valuable insights to demonstrate how a project of this scale was successfully executed and more value added to the development plans. The unique equipment layout comprised twin sea-submerged, skid-mounted electrical submersible pumps (ESPs), 6?? hoses, filtration unit, a chemical treatment unit, eight 500 bbl storage tanks, and a horizontal pumping system (HPS). The layout of the surface facility components, their performance and the importance of continuous water injection in addressing the test goals are discussed. The injection well performance was monitored by integrating Joshi's equation to Hall Plot and slope analyses to provide means of more meaningful use of injection pressure and rate data. The synergy of the mini-plant components coupled with engineered performance monitoring tools were enablers in this test design to help unlock more reserves. Overall, the test was a great tool to qualify field development plan assumptions, indicating that less powered water injectors than initially planned, are required Introduction Production from the carbonate field started several years ago from reservoir A with fluid and rock compressibilities being the primary drive mechanisms. Nearly 20 years later, production started from a lower reservoir Bb, and from reservoir Aa six years later. Due to low demand, it was subsequently shut-in. In all three reservoirs, (Aa, Ba and Bb) a continuous tar mat underlay the oil column and posed an uncertainty as to the extent it was sealing and effectively separating the oil column in the reservoirs from the underlying aquifer. Water injection was considered a priori since the assurance for an adequate natural water drive from the aquifer is low. With the present major development by means of peripheral matrix water injection as the planned pressure support mechanism, the tar mat created a potential challenge in assuring adequate pressure support for the field during production. Without an effective communication between the tar mat layer and the oil zone, with water flooding, a potential risk yet remains of leaving relatively high oil saturation pockets behind the flood front.
The M field development involves one of the largest drilling projects in Saudi Arabia, targeting various carbonate reservoirs, and with an extraordinary amount of extended reach wells (ERWs) requires meeting the expected oil production rate, at the lowest development cost possible. More than two-thirds of the wells fall under the extended reach drilling classification, and the majority of the wells have measured depths (MDs) between 24,000 ft and 31,000 ft. These wells are open hole completions where acid stimulation is highly needed to overcome reservoir damage and improve the well's performance after drilling operations terminate.The placement of the treatment fluids requires a uniform distribution along the open hole section. Among the different techniques considered, namely bullheading, using the rig drill pipe and coiled tubing (CT), the last one offered the soundest technical and cost option. However, the CT technique alone did not show the ability in reaching the maximum depth in most ERWs of this field. Therefore, the tractor 1 was required to provide the significant amount of pull force needed to operate inside these long distances, not seen before in open hole completions.The first eight well campaigns, using a combination of CT, a hydraulic tractor and friction reducer fluids, have achieved the main objectives. Moreover, a new intervention world record 2 was set when the CT bottom-hole assembly (BHA) reached the maximum depth of 28,257 ft inside open hole in two different occasions, to place the stimulation fluids, and to record an injection profile. During the campaign, a total of 41,774 ft accumulated footage has been operated with the tractor, allowing over 3,400 bbls of acid to be placed in direct contact with the formation. As a result, the average injection rate has increased more than tenfold, reducing the drilling requirements for injection wells originally projected.The job preparation, technology, results, learning curve experience and best practices are discussed in this paper, including proposed operational enhancements. This experience demonstrates the feasibility of the operations with CT required for full zone coverage, yielding optimum water injection rates at the lowest development cost.
Increases in well complexity and stimulation challenges have led to more complicated stimulations. The challenge that consistently arises after conceptually designing the treatment is how to determine the zonal coverage and evaluate the stimulation, especially in extended reach wells in carbonate reservoirs. Significant effort has been spent on using modern technologies to qualitatively evaluate zonal coverage and estimate the skin factor evolvement after the treatment. No work has yet answered the following question: How does matrix acidizing alter near-wellbore permeability and affect the zonation of the wellbore when treating carbonate reservoirs?In long horizontal wells that are drilled in carbonate formations, it is believed that wormholing significantly alters the near-wellbore apparent permeability. Nevertheless, methods to estimate the change in permeability resulting from a matrix treatment are not known, and usually the change is accounted for in simulators by assigning a very low skin value. Other work conducted in carbonate reservoirs using pressure transient analysis (PTA) techniques has shown that applying a change in permeability is necessary to obtain a type-curve match.This paper presents an innovative workflow and algorithm to estimate the changes in the critical matrix rock properties and how to incorporate these changes into further simulation. The algorithm integrates the while drilling mobility data, open hole porosity logs, pressure transient data, distributed temperature survey data, and production logging data to verify the accuracy of the model by using the flow rate as the control parameter for iterations.A case study shows how we could derive a flow profile for the pre-stimulation stage, optimize matrix stimulation treatments in real time according to the formation response and diversion efficiency, define reservoir zones that are contributing to flow before and after the treatment, and finally, estimate new values of permeability and skin to be utilized in post-treatment reservoir simulations.
Safeguarding and restoring the normal ecosystems and environment of the Arabian Gulf in an active hydrocarbon province undergoing field development is a tough challenge. Nevertheless, a multidisciplinary team involved in this field development has maintained a profound commitment in stewarding natural resources of the major carbonate field in Saudi Arabia. As part of the Kingdom's strategy to maintain crude oil production targets, production tests were needed to confirm potential of the wells in the Southern part of the field's structure prior to commissioning. The wells are located on drill sites in some artificial islands that were reclaimed from the sea. The six-well deliverability testing campaign should greatly enhance offshore field development, help to obtain reservoir characterization parameters, evaluate stimulation needs for producers, and assess comingling concept for selected wells. A total of 27 artificial Islands and a major transportation causeway were constructed by land reclamation from offshore waters of the Arabian Gulf. These facilitate onshore access to drill sites thus eliminating relatively more expensive fixed steel jacket rigs or platforms.Due to land space limitation and well spacing constraints on the drill sites, a compact well test facility layout was specifically designed to achieve smokeless flaring, full combustion, and minimize environmental impact. The design consists of two heat exchangers, three-phase separators, i-loop systems for effective H 2 S scavenging and chemical mix with crude, surge tanks and air compressors. When deployed, this system helped to meet the test objectives and addressed space limitation challenges, mitigated risk to sea pollution in a sensitive marine environment, and forestalled uncontrolled release of hydrocarbons to the environment.The completion of the cleanup and flow back operation on these wells with no single safety incident, uncontrolled release of hydrocarbons, or spill to nearby offshore waters was a major demonstration of leadership and a key contribution to well testing in similar environments. BackgroundMeeting global demands responsibly and reliably led to the company's development of the Y field close to the shoreline of the Arabian Gulf. Developing the prolific field is a crucial element in the company's energy supply strategy with a significant increment to the anticpated production levels within afew years. Due to the shallow water location, access to offshore drilling rigs would be impossible without extensively dredging offshore channels. The access challenge was handled by handled by building a causeway that connects to a series of artificial drilling islands. The primary causeway artery has +21 km total length with an additional +20 km of laterals. The laterals form branches of 25 islands designated for crude oil production. Two of the islands are dedicated for water injection to pressurize the field. The drilling islands and causeway were created from sand dredged from the seabed and protected with huge rocks around the slopes. Ju...
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