Stimulation of Seawater Injectors by GLDA (Glutamic-Di Acetic Acid)

Mohamed Mahmoud; K. Z. Abdelgawad; S. M. Elkatatny; A.. Akram; T.. Stanitzek
Presented at SPE Drill & Compl 31 (03): 178–187.


Seawater is injected to maintain the reservoir pressure that supports the oil production from carbonate and sandstone reservoirs. In certain regions, the seawater contains more than 4,000 ppm sulfate, and the formation contains more than 19,000 ppm calcium; this will cause calcium sulfate precipitation at the reservoir conditions. The precipitate at the reservoir conditions will be anhydrite, and it will cause formation damage that will reduce the well injectivity. Stimulation treatments are required to recover the well injectivity; this requires stopping water injection to perform the stimulation treatments, and also it requires flowing back the well after stimulation treatment. In this study, we are proposing a new method that we can use to stimulate water injectors without stopping the water injection. The new method includes adding a chelating agent to the injected seawater at the wellhead at 15 wt% concentration. The fluid will be injected at the surface with the seawater with a specific dose to achieve the required concentration. Several solubility and coreflooding tests were performed with actual carbonate cores and GLDA (glutamic-di acetic acid) chelating agent at different temperatures. The chemical injection does not need coiled tubing and can be injected at the surface with the seawater. The chelating agents will sequester all calcium in solution and will prevent the calcium sulfate precipitation. GLDA chelating agent will be used with seawater, with no need to use treated or fresh water. Also, flowing back the well is not required because the fate of GLDA in the aquifer is soluble. Solubility tests up to 250°F at high pressure showed that the GLDA is stable with seawater. Coreflood experiments and computed-tomography scans showed the ability of GLDA in the creation of dominant wormholes through 6- and 1.5-in. carbonate cores at 212 and 150°F, respectively. GLDA chelating agent can be used to stimulate seawater injectors without additives because this chemical is stable and mild with the well tubulars. Previous corrosion studies on GLDA showed that its corrosion rate is in the allowable range without adding corrosion inhibitors.