Drilling hydrocarbon formations where hydrogen sulfide (H 2 S) is present could lead to the carryover of H 2 S with the drilling mud (i.e., drilling fluid) to the surface, exposing working personnel to this lethal gas. Additionally, H 2 S is very corrosive, causing severe corrosion of metal parts of the drilling equipment, which in turn results in serious operational problems. The addition of an effective H 2 S scavenger(s) in the drilling mud formulations will overcome these health, safety, and operational issues. In this work, zinc oxide (ZnO), which is a common H 2 S scavenger, has been incorporated into waterbased drilling mud. The H 2 S scavenging performance of this ZnOcontaining drilling mud has been assessed. Additionally, drilling mud formulations containing either copper nitrate (Cu(NO 3 ) 2 •3H 2 O) or potassium permanganate (KMnO 4 ) have been prepared, and their H 2 S scavenging performances have been studied and compared to that of the ZnO-containing drilling mud. It has been observed that the scavenging performance (in terms of the H 2 S amounts scavenged up to the breakthrough time and at the saturation condition) of the ZnO-containing drilling mud is very poor compared to those of the copper nitrate-containing and KMnO 4 -containing drilling muds. For instance, the amounts of H 2 S scavenged up to the breakthrough time by ZnO-containing, copper nitrate-containing, and KMnO 4 -containing drilling muds were 5.5, 15.8, and 125.3 mg/g, respectively. Furthermore, the amounts of H 2 S scavenged at the saturation condition by these drilling muds were, respectively, 35.1, 146.8, and 307.5 mg/g, demonstrating the superiority of the KMnO 4 -containing drilling mud. Besides its attractive H 2 S scavenging performance, the KMnO 4 -containing drilling mud possessed more favorable rheological properties [i.e., plastic viscosity (PV), yield point (YP), carrying capacity of the drill cuttings, and gelling characteristics] relative to the base and the ZnO-containing and copper nitrate-containing drilling muds. The addition of KMnO 4 to the base drilling mud increased its apparent viscosity, PV, and YP by 20, 33, and 10%, respectively. Additionally, all tested drilling muds possessed acceptable fluid loss characteristics. To the best of our knowledge, there are so far no published studies concurrently tackling the H 2 S scavenging (i.e., breakthrough time, breakthrough capacity, saturation time, saturation capacity, and scavenger utilization) and the rheological properties of water-based drilling muds, as demonstrated in the current study, highlighting the novelty of this work.
Sandstone acidizing is the process of removing the damage from sandstone reservoirs to restore the well productivity/injectivity to its original or expected rates. It differs from carbonate acidizing in which a substantial portion of the rock is dissolved. Stimulating sandstone with mud acid HF/HCl may cause many problems as sandstone is a clastic sedimentary rock that consists mainly of quartz, silica minerals, feldspars, clays, and minor quantities of zeolite and chlorites. When conventional mud acid reacts with rock some sensitive components of sandstone get cemented by silica, calcite, or iron oxides. This happens due to the different precipitation reactions that take place and form fluosilicates, calcium fluorides, silica-gel filming, and even colloidal silica-gel compounds. In this work, two chelating agents, hydroxyethylenediaminetetraacetic acid (HEDTA) and diethylenetriaminepentaacetic acid (DTPA), were used to stimulate Berea sandstone cores. Berea sandstone cores were scanned using the XRD to quantify their mineralogical composition. Different pore volumes of 0.6M HEDTA and 0.6M DTPA were used as a preflush followed by different concentrations of HF as a main flush. For the post-flush stage, ammonium chloride was used to flow back the cores and measure their permeability. The levels of calcium, magnesium, aluminum, and iron ions in the effluent samples were measured using inductively coupled plasma (ICP) to assess the ability of each chemical to leach these different ions. Both HEDTA and DTPA showed a strong capability of chelating calcium, iron, and magnesium ions from the sandstone cores while the amounts of chelated aluminum ions were quite small. Once starting the injection of the used chelating agents, the permeability of the core got enhanced gradually. The higher amounts of the chelating agents resulted in better the cores permeability. However, DTPA showed a better permeability enhancement than HEDTA due to its stronger ability to chelate the calcium, iron, magnesium, and aluminum ions. Adding HF as the main flush initiates different reactions with the clay and silica minerals of the Berea sandstone cores. This caused a reduction in the permeability due to the formation of some precipitates such as fluosilicates and calcium fluorides. Therefore, it is recommended to use a very low concentration of HF while treating the Berea sandstone.
In this study, an in situ-generated hydrofluoric acid (HF) was used for sandstone acidizing, where an acid precursor (ammonium fluoride NH 4 F) reacted with a suitable oxidizer (sodium bromates NaBrO 3 ) in an exothermic reaction. First, the new chemical mixture was prepared to react with pure quartz samples and the reaction effluent was analyzed to identify the presence of Si + ions using the inductively coupled plasma (ICP) technique. Core flooding experiments were performed using Gray Berea sandstone cores (6 in. length and 1.5 in. diameter). A preflush stage of 5 PV of 7 wt % HCl was injected to remove any calcite content in the core. The main chemicals were then flushed for 3 successive cycles of 1 PV each. To assure core integrity, scratch tests and NMR scans were run on the core sample before and after the treatment. The new chemical mixture could dissolve the quartz sample and reduce its weight by 80 mg. The concentration of the dissolved Si + ions was more than 90 ppm. This proves the capability of the chemical mixture to generate HF. The initial core permeability was measured at a stabilized flow rate of 2 cm 3 /min to be 33 mD. After the acid preflush stage, the core permeability reduced to 31 mD. Core permeability increased immediately after the first treatment cycle and reached 41 mD. At the end, the core flooding results showed a permeability improvement for Gray Berea sandstone cores by almost 40%. The ICP analysis of the effluent showed a total amount of chelated Si + ions of about 10.5 mg. In addition to the high temperature generated in the near-wellbore area, the pressure increased because of the produced nitrogen gas from the exothermic reaction and reached about 600 psi. The scratch test showed an increase in the sample uniaxial compressive strength from 7432 to 9235 psi. The dynamic Poisson's ratio and the dynamic Young's modulus increased as well from 0.17 to 0.19 and from 2159 to 3585 ksi, respectively. The enhancement in the mechanical properties of the core can be attributed to the presence of the potassium element in Berea cores and its solidification reaction with the HF generated. The NMR measurements of the core sample before and after the acidizing process show an increase in the core porosity; however, the core preserved its original pore system. Upon application of this new stimulation technology, the true production potential of sandstone reservoirs can be achieved, well tubular corrosion will be minimized, and handling hazardous chemicals such as HF will be avoided. Most importantly, controlling the reaction rate, by controlling the amount of exothermic chemicals, can ensure deep acid penetration as well.
The effect of increasing BaO on the intensity and position of absorption bands induced in barium silicate glasses was studied. Many of these glasses showed a two‐step process in the growth and thermal bleaching curves. This process was attributed to two types of defects in the glass, induced and intrinsic. Infrared absorption, molar volume, and X‐ray diffraction studies predicted structural changes at compositions containing about 22.5 and 27.5 mole % BaO. The results of gamma‐induced absorption were in Une with these predictions, supporting the view that color center studies can be used to detect changes in structure, especially when high radiation doses are applied.
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