Summary Matrix acidizing is used in carbonate formations to create wormholes that connect the formation to the wellbore. Hydrochloric acid (HCl), organic acids, or mixtures of these acids are typically used in matrix-acidizing treatments of carbonate reservoirs. However, the use of these acids in deep wells has some major drawbacks, including high and uncontrolled reaction rates and corrosion to well tubulars, especially those made of chromium-based tubulars (Cr-13 and duplex steel); and these problems become severe at high temperatures. To overcome problems associated with strong acids, chelating agents were introduced and used in the field. However, major concerns with most of these chemicals are their limited dissolving power and negative environmental impact. L-glutamic acid diacetic acid (GLDA), a newly developed environmentally friendly chelate, was examined as a replacement for acid treatments in deep oil and gas wells. The solubility of calcium carbonate (CaCO3) in the new chelate was measured over a wide range of parameters. Coreflood tests were conducted using long Indiana limestone cores 1.5 in. in diameter and 20 in. in length, which allowed better understanding of the propagation of this chemical in carbonate rocks. The cores were X-ray scanned before and after the injection of chelate solutions into the cores. The concentration of calcium (Ca) and chelate was measured in the core effluent samples. To the best of our knowledge, this is the first study to examine the fate and propagation of chelating agents in coreflood studies. GLDA has a very good ability to dissolve Ca from carbonate rocks over a wide pH range by a combination of acid dissolution and chelation. The addition of 5 wt% sodium chloride (NaCl) did not affect the GLDA performance at pH = 13 but significantly accelerated the reaction at pH = 1.7. Compared with other chelating agents, GLDA dissolved more Ca than ethanoldiglycinic acid (EDG) but less than hydroxyethyl ethylenediamine triacetic acid (HEDTA) at high pH values. GLDA of pH = 1.7 was able to form wormholes at 2 and 3 cm3/min. GLDA was found to be thermally stable at temperatures up to 350°F.

Carbonate minerals are present in sandstone formations. These minerals are either introduced to the formation during drilling/completion operations or naturally present in the rock. There is a need to remove these carbonates to enhance well performance. This especially true if there is a need to use HF-based fluids to prevent the precipitation of calcium and magnesium fluorides.In this study, we introduced GLDA (L-glutamic acid-N,N-diaceticacid) a new environmentally friendly chelate to remove carbonate minerals from sandstone formations. We also compared its performance with available chelates like EDTA (ethylenediaminetetraaceticacid) and HEDTA (hydroxyethylenediaminetriaceticacid). Berea (5 wt% clays) and Bandera (11 wt% clays) sandstone cores were used in the coreflood experiments. The concentration of the chelates used was 0.6M at pH values of 11 and 4. The coreflood experiments were run at a flow rate of 5 cm 3 /min and 300 o F.Coreflood experiments showed that at high pH values (pH =11) GLDA, HEDTA, and EDTA were almost the same in increasing the permeability of both Berea and Bandera sandstone cores. GLDA, HEDTA, and EDTA were compatible with Bandera sandstone cores. The weight loss from the core was highest in case of HEDTA and lowest in case of GLDA at pH 11. At pH 4, 0.6M-GLDA performed better than 0.6M HEDTA in the coreflood experiments. The permeability ratio (final/initial) for Bandera sandstone cores was 2 in the case of GLDA and 1.2 in the case of HEDTA at pH of 4, and 300 o F. At pH 11, HEDTA, EDTA, and GLDA almost were the same in enhancing the permeability of the Bandera sandstone cores. At pH value of 4, GLDA gave the best results in Berea and Bandera sandstone cores.

Summary Matrix acidizing is used in carbonate formations to create flow channels from the formation to the wellbore; in sandstone formations, however, the goal is to dissolve materials that impair well performance. However, the use of acids in deep wells has some major drawbacks, including high reaction rate and corrosion to well tubulars. We have discovered a new stimulation chemical that can be used as a replacement for or in combination with acid treatments in deep wells. A polyacid whose structure allows for acidification is described. The polyacidic chelate L-glutamic acid, N, N-diacetic acid (GLDA) is manufactured from L-glutamic acid (MSG). The chelate-based fluid very effectively dissolves CaCO3, and it is less corrosive to the equipment and easy to handle. This paper discusses the reaction of the new chelate, GLDA, with calcite and compares its performance with other available chelates, including ethylenediaminetetraacetic acid (EDTA), hydroxy-ethylethylenediaminetriacetic acid (HEDTA), nitrilotriacetic acid (NTA), and ethanoldiglycine (EDG). GLDA dissolves calcite over a wide pH interval, although it is less effective than HEDTA at pH > 5. A unique property of GLDA is its high solubility; solutions exceeding 40 wt% can be achieved at a pH of approximately 2, whereas HEDTA solubility is limited to approximately 10 wt%. A mole of GLDA with a natural pH of approximately 1.5 is capable of dissolving up to two moles of CaCO3. Throughout the pH range, GLDA appears to be as thermally stable as HEDTA. As an additive to hydrochloric acid (HCl), GLDA is as effective as HEDTA in preventing precipitation of moderate levels of Fe3+ in spent acids. At high Fe3+ concentrations, GLDA is slightly less effective than HEDTA on a molar basis; but, to deal with high Fe3+ levels, GLDA may be better because significantly higher concentrations of it are possible in various acids. In 28 wt% HCl, HEDTA has limited solubility while GLDA's solubility exceeds 40 wt%. From an environmental standpoint, GLDA is readily biodegradable and is made from a renewable raw material, monosodium glutamate. GLDA has low toxicity and aquatic toxicity characteristics. As a replacement for HCl, GLDA is significantly safer and less corrosive.

Chelating agents are used to remove various inorganic scales, including sulfates and carbonates. They are also used as stand-alone stimulation fluids and as iron control agents during acidizing treatments. The main chelating agents used in the field, include: ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), N-(hydroxyethyl)-ethylenediamineteriaacetic acid (HEDTA), and recently, L- glutamic acid-N, N diacetic acid (GLDA). One of the concerns with these chelates is their thermal stability at elevated temperatures. A few studies examined the thermal stability of these chelating agents, and the impact of thermal degradation products on permeability. The objectives of the present study are to: 1) Examine the thermal stability of several chelating agents and their salts up to 450°F, and 2) assess the effect of thermal decomposition products on the permeability of carbonate and sandstone cores with different initial permeabilities. We prepared solutions (0.4 to 0.6 M) of HEDTA, GLDA, NTA, EDTA and their salts. The solutions of these chelates were heated at various temperatures and times (2 to 12 hrs.). The concentration of chelate was determined using a new analytical technique that was based on titration with FeCl3. The products of thermal decomposition of chelates were determined using MS technique. Core flood tests were conducted on Berea sandstone and Indiana limestone to determine the effect of thermal degradation products on the permeability of these cores. Coreflood tests were conducted at 325°F and 3 cm3/min. Most chelates decomposed at temperatures greater than 350°F. Among monovalent salts, potassium salt was found to be the most stable one. Chelates with two nitrogen atoms were more stable than those with one nitrogen atom. For example, diammonium salt of EDTA is more stable than diammonium salt of GLDA. Analyses of chelate solutions after heating using MS technique highlighted that the decomposition products included: iminodiacetic acid, formic acid, and α-hydroxy acids. Results of the coreflood indicated that some of the thermal decomposition products can cause formation damage. This paper will summarize the results obtained, and explain how chelates can be used to improve field treatments, especially at high temperatures.

The objective of stimulation of sandstone reservoirs is to remove the damage caused to the production zone during drilling or completion operations. Many problems may occur during sandstone acidizing with HCl/HF mud acid. Among these problems: decomposition of clays in HCl acids, precipitation of fluosilicates, the presence of carbonates can cause the precipitation of calcium fluorides, silica-gel filming, colloidal silica-gel precipitation.In this study, a recently introduced chelating agent, glutami-N,N-diacetic acid(GLDA), was used to stimulate sandstone cores. Berea sandstone cores with 8 wt% clays content were used in this study. Different GLDA solution pH values (1.7 -13) were used in the coreflood experiments. The sandstone cores were scanned before and after the treatment to investigate the effect of GLDA on the core. The effluent samples were analyzed for calcium, magnesium, aluminum, and iron using the ICP to assess the ability of GLDA on the complexation of these ions. Coreflood experiments were run at temperatures of 200 to 300 o F and the concentration of GLDA was determined after the treatment. The effects of injection rate, volume of GLDA, temperature, and GLDA initial pH value were investigated on the Berea sandstone cores in the coreflood experiments. Different correlations were used to determine the core permeability after the treatment, and the correlation that gave the minimum error was determined.GLDA showed a strong ability in chelating calcium, iron, magnesium, and it chelated small amounts of aluminum ions from the sandstone cores. At 300 o F, GLDA at different pH values was able to enhance the core permeability. Decreasing the injection rate from 5 to 2 cm 3 /min increased the contact time between the fluid and the rock and increased the amount of dissolved ions. Xray CT scan showed a porosity increase after the treatments at different conditions. The concentration of GLDA after the coreflood experiment was almost the same before the treatment showing a high thermal stability up to 300 o F in the coreflood experiment. Labrid was found to be the best correlation to predict for the core permeability after treating Berea sandstone cores by 20 wt% GLDA solutions.

Matrix acidizing is used in carbonate formations to create flow channels from the formation to the well bore, whereas in sandstone formations the goal is to dissolve materials that impair the well production. However, the use of acids in deep wells has some major drawbacks including high reaction rate and corrosion to well tubulars. We have discovered a new stimulation chemical that can be used as a replacement for or in combination with acid treatments in deep wells. A polyacid whose structure allows for acidification is described. The polyacidic chelate L-glutamic acid, N, N-diacetic acid or GLDA is manufactured from L-glutamic acid (MSG). The chelate-based fluid very effectively dissolves CaCO3 and it is less corrosive to the equipment and easy to handle. This paper discusses the reaction of the new GLDA chelate with calcite and will compare its performance with other available chelates, including EDTA, HEDTA, NTA and EDG. GLDA dissolves calcite over a wide pH interval, although it is less effective than HEDTA at > pH 5. A unique property of GLDA is its high solubility - solutions exceeding 40 wt% can be achieved at a ~ pH 2 where HEDTA solubility is limited to ~ 10 wt%. A mole of GLDA acid with a natural ~ pH 1.6 is capable of dissolving up to two moles of CaCO3. Throughout the pH range GLDA appears to be as thermally stable as HEDTA. As an additive to HCl, GLDA is as effective as HEDTA in preventing precipitation of moderate levels of Fe in spent acids. At high Fe concentration GLDA is slightly less effective than HEDTA on a molar basis - but to deal with high Fe GLDA may be better as significantly higher concentrations of it are possible in various acids. In 28 wt% HCl, HEDTA has limited solubility while GLDA's solubility exceeds 40 wt%. From an environmental standpoint GLDA, is readily biodegradable and is made from a renewable raw material - monosodium glutamate. GLDA has low toxicity and aquatic toxicity characteristics. As a replacement for HCl acid, GLDA is significantly safer and is less corrosive.

Summary Different chelating agents were used as alternatives for hydrochloric acid (HCl) in matrix acidizing to create wormholes in carbonate formations. Previous studies demonstrated the use of ethylenediaminetetraacetic acid (EDTA), hydroxy ethylenediaminetriacetic (HEDTA), and glutamic acid-N,N-diacetic acid (GLDA) as standalone stimulation fluids to stimulate carbonate reservoirs. The main problem of using EDTA and HEDTA is their low bio-degradability. GLDA was introduced as a standalone stimulation fluid for deep carbonate reservoirs where HCl can cause corrosion and face dissolution problems. In this study, calcite cores 1.5 in. in diameter and 6 or 20 in. in length were used to determine the optimum conditions where the GLDA can break through the core and form wormholes. GLDA solutions with pH values of 1.7, 3, and 3.8 were used. The optimum conditions of injection rate and pH were determined using coreflood experiments. Damköhler number was determined using the wormhole length and diameter from the CT scan 3D and 2D images. GLDA was compared with chelates that are used in the oil industry such as EDTA and HEDTA. GLDA also was used to stimulate parallel cores with different permeability ratios (up to 6.25). GLDA was found to be very effective in creating wormholes at pH = 1.7, 3, and 3.8; at different injection rates; and at temperatures up to 300°F. Increasing the temperature increased the reaction rate and less volume of GLDA was required to break through the core and form wormholes. Unlike HCl, in GLDA there was no face dissolution or washout in the cores even at low injection rates (0.5 cm3/min). An optimum injection rate and Damköhler number were found at which the pore volume (PV) required to create wormholes was the minimum. GLDA at pH 1.7 and 3 created wormholes with a small number of PV (at 1 cm3/min, GLDA at pH 1.7 required 1.5 PV at 300°F, and at pH 3 it required 1.8 PV). Compared with acetic acid, the volume of GLDA at pH 3 required to create wormholes was less than that required with acetic acid at the same conditions. GLDA was found to be effective in stimulating parallel cores up to 6.25 permeability contrast (final permeability/initial permeability).

Matrix acidizing is used to remove near wellbore damage and create channels or wormholes in carbonate formations to improve well performance. The use of conventional matrix acidizing fluids with HCl is not effective in some cases because of the rapid acid spending. Previous studies have demonstrated the use of chelates such as ethylenediaminetetraacetic acid (EDTA) and N-hydroxyethylenediaminetriacetic acid (HEDTA) as alternatives for HCl to stimulate carbonate reservoirs. A recently introduced chelating agent was examined to stimulate deep carbonate reservoirs. This chelating agent can be used at very low injection rates to avoid fracturing the target zone during the treatment, which may occur if HCl is used at high flow rates. The chelating agent used in this study was glutamic acid-N, N-diacetic acid (GLDA). Two sets of calcium carbonate cores were used one with 1.5 in. diameter and 20 in. length and the other set was 1.5 in. diameter and 6 in. length. Calcium carbonate cores such as Indiana limestone cores were used in this study. A dolomite core 1.5 in. diameter and 6 in. length was used to investigate the ability of this chelating agent to stimulate dolomite cores. The cores were treated with GLDA at various pH (1.7–13) and temperatures (180–300°F). The concentrations of dissolved calcium, magnesium, and GLDA in the core effluent were measured for material balance determination. GLDA was found to be highly effective in creating wormholes over a wide range of pH (1.7–13) in calcite cores. Increasing temperature enhanced the reaction rate, more calcite was dissolved, and larger wormholes were formed for different pH with smaller volumes of GLDA solutions. In addition, GLDA was very effective in creating wormholes in the dolomite core as it is a good chelate for magnesium. GLDA was found to be equally effective in creating wormholes in short and long cores.