This paper will discuss the largest coiled tubing acid stimulation operation completed on a water injection well in Saudi Arabia. Stimulation design, field execution and the well performance before and after the treatment as well as massive planning, logistics and coordination are the key elements of this discussion. Furthermore, the authors would like to briefly review the future plans for other long/ multilateral wells in the area.
This job was conducted on a dual lateral horizontal power water injector. The objective of this job was to stimulate the formation of both laterals by pumping 20% hydrochloric acid (HCL) and 20% strength diesel-emulsified acid and diverting it with 20% viscoelastic surfactant based acid on using Coiled Tubing (CT) and a Multilateral Tool (MLT). A total of 10,335 ft horizontal interval was successfully stimulated with 362,700 gallons of treatment fluid in 27 stages using 2 3/8" CT. On this job the MLT was successful in locating each lateral. The post-acid injection rate has been increased by more than double, higher than initial expectations. Consequently, the injectivity index has been increased drastically above the field average.
Based on success of this stimulation job, the concept of designing and treating other Maximum Reservoir Contact (MRC) injectors using this technique becomes a recommended intervention process. The key to enhance future jobs lies on the ability to effectively capture and use the lessons learned from this massive operation. The continuous success of these jobs will help to improve the water injection system in Ghawar field and will enhance oil recovery.
Background
Saudi Aramco drilling strategy has been rapidly progressing through several sequences in order to optimize the oil production, water injection and cost. Accordingly, a new generation of wells are being widely drilled and completed with multiple legs or laterals in the horizontal section of the desired formation. This type of horizontal well has been implemented in the Ghawar field.
Although multilateral wells have proven their efficiency to meet the strategy, the complexity of well intervention becomes a challenge for Operating and Service Companies. Logging, stimulation and other downhole surveys are major and difficult tasks.
Currently the situation is better and the well intervention work can be conducted on an individual lateral as a result of utilizing the MLT re-entry tool. It depends on mechanical and pressure differential without an electric line or guidance system. Also, it can be used in conjunction with other CT downhole tools.
Case History
Well-A is a Power Water Injection (PWI) well which was drilled in 2002 as a dual-lateral horizontal open hole to have a maximum reservoir contact and support oil production in a carbonate reservoir which is a relatively tight formation. The well was drilled with two laterals across Arab-D Zone 2A. The 6 1/8" main bore, lateral 1, was drilled to a Total Depth (TD) of 13,649 ft Measured Depth (MD) and lateral 2 was drilled to a TD of 13,676 ft MD. The 7" liner was set at 7,686 ft while the window depth is at 8,720 ft (see Fig.1 below).
Job Justification
The objective was to acidize the carbonate formation of both horizontal laterals by pumping plain 20% HCL acid and diesel-emulsified 20% HCL (SXE) acid and diverting it with viscoelastic diverting 20% HCL acid (VDA) using a Coiled Tubing Unit (CTU) and MLT.
