Using high- and low-salinity seawater injection to maintain the oil reservoir pressure without damage

Abstract

The oil reservoir pressure declines due to oil production, and this decline will lead to reduction in the oil productivity. The reservoir pressure maintenance is a practice in the oil industry in which seawater is injected into the aquifer zone below the oil zone to support the reservoir pressure. Calcium sulfate scale is one of the most serious oilfield problems that could be formed in sandstone and carbonate reservoirs. Calcium sulfate may precipitate during the injection of seawater with high sulfate content into formation brine with high calcium content. Mixing seawater and formation water may cause precipitation of calcium sulfate, barium sulfate, and/or strontium sulfate. Seawater treatment does not remove the entire sulfate ions from the injected water. Low sulfate concentrations may cause damage. Enhanced oil recovery processes such as smart water injection, which originally is diluted seawater, may cause calcium sulfate precipitation as the reduction of water salinity will increase the sulfate precipitation and decrease its solubility. This study was conducted to investigate the damage caused by the deposition of calcium sulfate precipitation. A solution is proposed to prevent the damage due to calcium sulfate by using chelating agents. Several coreflooding experiments were conducted using Berea sandstone and Indiana limestone cores at reservoir conditions of pressure and temperature using seawater (high and low salinity) and formation water. Chelating agents used in this study are: EDTA (ethylenediaminetetraacetic acid), HEDTA (hydroxyethylenediaminetriacetic acid), and HEIDA (hydroxyethyliminodiacetic acid). HEDTA and HEIDA chelating gents are environmentally friendly and can be used in marine environment. High-salinity water injection caused severe formation damage, and the injectivity will decline faster compared to the low-salinity water injection. HEDTA and EDTA chelating agents at low concentrations performed better than HEIDA chelating agents in both Berea sandstone and Indiana limestone cores. HEDTA and EDTA chelating agents were able to prevent the damage due to calcium sulfate precipitation and enhanced the core permeability.

Metagenomic Investigation of a Low Diversity, High Salinity Offshore Oil Reservoir

“…Barium, calcium, magnesium and strontium were also reported at higher concentrations than other metals in the samples at 594 mg/L (4.33 mM), 5434 mg/L (135.60 mM), 2005 mg/L (82.51 mM) and 633 mg/L (7.22 mM), respectively. These high metal concentrations remain within the range reported in other oil reservoir formation waters [39][40][41].…”

An electrochemical and X-ray computed tomography investigation of the effect of temperature on CO2 corrosion of 1Cr carbon steel

“…Seawater injection, amongst the other, is one of the most common EOR techniques for offshore oil fields [28] [29]. With time, the water fraction in the produced fluid can reach levels of 95% or higher, increasing the contact between tube materials and electrolyte [30].…”

Novel chemical stimulation for geothermal reservoirs by chelating agent driven selective mineral dissolution in fractured rocks

“…Among the various kinds of chelating agents, environmentally friendly compounds such as N -(2-hydroxyethyl)ethylenediamine- N , N′ , N′ -triacetic acid (HEDTA) and N, N -bis(carboxymethyl)- l -glutamic acid (GLDA) are well suited to chemical stimulation 31 , 32 . A previous study examined the use of HEDTA solution of pH 2.5, 4, and 9 to stimulate carbonates at approximately 150 °C, and reported that the use of HEDTA at pH 4 was effective 33 .…”