Microbial metabolic activity of drilling waste

Operations conducted by petroleum industry generate an entire range of drilling waste. The chemical composition of drilling waste and its toxicity depend primarily on the geological and technological conditions of drilling, the type of drilled rock deposits and on the type and composition of the drilling mud used. In the course of drilling operations, drilling fluids are in constant contact with bacteria, fungi and other organisms infecting the mud. Pioneer species, capable of surviving and using the resources of this specific environment, are selected. For this reason, the effectiveness of microbiota survival on different types of spent drilling muds and in different dilutions with brown soil was measured. Spent drilling muds samples came from drilling operations in various regions of Poland, e.g. Subcarpathia, the Polish Lowland and Pomerania regions. Oxygen consumption after 96 h was around 20 μg·g‒1 dry mass in soil or soil/drilling water-based mud mixture. Soil mixes contained 10 wt% synthetic base, mud had a higher oxygen consumption – 38 μg · g‒1 dry mass. Oxygen consumption decreases sharply as the content of the spent synthetic base mud fraction increases. A higher concentration of spent SBM (35 wt%) reduced the aerobic metabolism by slightly more than 50%. A high concentration of reduced carbon decreased the respiratory quotient (RQ) value to 0.7. All the researched drilling waste shows microbiological activity. At the full concentration of drilling fluids and non-dilution options, the chemical composition (salinity, inhibitors, etc.) strongly inhibits microbiota development and consequently, respiration. 34 A. Jamrozik, R. Żurek, A. Gonet, R. Wiśniowski Some organic polymers (starch, carboxymethyl cellulose) are easily decomposed by bacteria or fungi (Behera et al. 2014). In the course of drilling operations, drilling fluids and then spent drilling mud are in constant contact with bacteria, fungi and other organisms infecting this mud. This biological contamination is accidental. Only strong microorganisms which can adapt to the existing conditions will survive in a given drilling fluid. In this sense, the spent mud environment predetermines the organisms. Pioneer species, capable of surviving and using the resources of this specific environment, are selected. The colonization of soil-spent drilling mud mixes containing semi-natural and natural polymers e.g. starch, partially hydrolyzed acryloamide, guar gum, and cellulose, has been rarely analyzed. For this reason, we measured the effectiveness of microbiota survival on different types of spent drilling mud and in different dilutions. Experimental analysis Materials The following spent drilling mud types were analyzed: 1. WBM: bentonite (1), chloride-polymeric (2), polymeric-triple inhibited (3), potassium-polymeric (4), polymeric-chloride-inhibited (5), salt-barite (6),and 2. SBM (7). Bentonite mud – K-1/B (1) is an aqueous suspension containing minimum 5wt.% bentonite API. Prior to adding bentonite to water, it was softened with 0.15wt.% sodium carbonate, and 0.3wt.% low-viscosity carboxymethyl cellulose (CMC LV) was also added. Polymeric-chloride mud – K-1/P-Cl (2) was applied in a depth interval 300 – 3,280 m. It was based on 30wt.% bentonite mud from the previous interval. The filtration of the mud was lowered with 1.0wt.% low-viscosity carboxymethyl cellulose (CMC LV) and 0.3wt.% low viscosity polyanionic cellulose (PAC LV). The rheological parameters were regulated with 0.3wt.% biopolymer Xhantan Gum (XCD Polymer) and 0.5wt.% high viscosity polyanionic cellulose (PAC R). The hydration of drilled clayey rocks was reduced with potassium chloride (~7.0wt.%) and partly hydrolyzed polyacrylamide PHPA (max 0.5wt.%). 0.1wt.% of triazine derivative was used as a biocide. Triple inhibited polymeric mud – W-2 (3) – clayey rock hydration was inhibited by KCl (4.5wt.%) and polyglycol (2.0wt.%). Moreover, the mud consisted of the following polymers: PHPA (0.3wt.%), XCD Polymer (0.2wt.%), PAC (0.6wt.%), CMC LV (1.0wt.%), carboxymethyl starch (1.0wt.%), biocide (0.1wt.%), sodium hydroxide (0.45wt.%), and biocide (~0.1wt.%). Potassium-polymeric mud – KRAM-1/K (4) consisted of KCl, NaCl, PHPA (0.3wt.%), liquid poliamine (3.0wt.%), low-molecular-weight acrylamide copolymer (0.65wt.%), poliglicol (max. 3.0wt.%), and biocide (~0.1wt.%). Inhibited polymeric-chloride mud – W-1/Cl-P (5), was based on potassium-polymeric mud with KCL, and PHPA (0.55 wt.%) as inhibitors. Filtration was regulated with PAC (0.6wt.%), CMC (1.2wt.%), XCD Polymer (0.2wt.%) and starch agents. Mud also consisted of sodium hydroxide, caustic soda, sodium carbonate and acidic sodium carbonate and barium (as a weighing agent) and 0.1wt.% of triazine derivative was used as a biocide. Saline-barite mud – L-2K (6) based on NaCl, consisted of barite, high temperature-resistant synthetic polymers (0.5wt.%), XCD Polymer (max. 0.6wt.%), modified starch (1.2wt.%) and salts in the form of sodium carbonate and acidic sodium carbonate, caustic soda and calcium, biocide (~0.1wt.%). SBM – PO (7) – inverse emulsion (‘water in oil’), based on paraffin oil containing hydrocarbons C13–C17 (57wt.%). Mud also contained organophilic clays, gilsonite, calcium hydroxide, calcium chloride, emulsifiers, cellulose (1.0wt.%), barite (30–60wt.%) and water. The spent drilling mud samples came from drilling operations in various regions of Poland, e.g. Subcarpathia, the Polish Lowland and Pomerania regions. They were collected from various wells and at various depths (90 m to 5040 m). The general characteristics of spent drilling mud are given in Table 1. The content of dry mass varied from 37.38 to 83.2%. The reaction (pH) ranged from 8.1 to 8.7, excluding sample W-2, for which the reaction was 9.90. The salinity of the samples characterized by electrolytic conductivity was high, 110 to 240 mS/cm, excluding sample K-1/B with 6.43 mS/cm. SBM, sample P-O, was low in Clions in the water extract – 1.443 g/dm3, and pH equaled 8.86. A majority of chlorides in the organic phase suspension were not extracted by water. Only after demulsification the Clconcentration in eluate grew to 28,500–55,000 mg/dm3 (Jamrozik et al. 2017). The microbiological activity of the spent muds was tested on samples with a brown soil admixture. The parameters of brown soil used in the dilution were as follows: phosphors (P) 0.207 mg·g‒1, total nitrogen (Kjeldahl methods) 1.60 g·kg‒1, total carbon 13.6 g·kg‒1 (0.11 %), and, the C/N ratio was 8.5. Brown soil used as a reference sample was not sterilized but used in the air-dry state, then sprinkled with water as other samples. Table 1. Spent drilling mud and its basic parameters Sample code Type and origin of drilling mud Specifi c gravity [g/cm3] Content of dry mass [%] Electrolytic conductivity of fi ltrates [mS/cm] pH of fi ltrates Concentration of Cl-, [g/dm3] K-1/B Bentonite 1.28 74.44 6.43 8.31 0.8 K-1/P-Cl Chloride-polymer 1.23 69.74 112 8.32 26 W-2 Polymer inhibited 1.26 68.25 90.2 9.90 40 KRA-1/K Potassium-polymer 1.51 55.86 204 8.44 9.1 W-1/Cl-P Chloride-polymer inhibited 1.28 68.87 171 8.10 90 L-2K Saline-barite 2.20 37.38 240 8.70 202 P-O SBM 2.34 53.00 5.14 8.86 1.4 Microbial metabolic activity of drilling waste 35 Methods For identifying mineral components in the spent drilling mud samples and checking for the presence of organic admixtures, analyses were conducted with use of the Fourier absorption spectroscopy in infrared (FTIR) with a spectrometer produced by the Bio-Rad Analytical Instrument, model FTS 165. The device operated in the following conditions: – measurement range 4,000 do 400 cm-1, – 4 cm-1, spectral resolution – transmission – pills with KBr. Mineral phases were identified by ascribing particular absorption bands to minerals, based on the reference spectra listed in the H. Moehke catalog. The microbiological activity was measured using the Columbus Instruments Micro-Oxymax flow respirometer, at room temperature. The samples with a dry weight of 7 g were placed into a 50 ml glass chamber, sprinkled with distilled water and exposed in a thermostated water bath at 20°C for 96 h. The sampling interval was 1 hour. The duration of the measurements was limited to 96 hours as the rate of respiration slowly dropped with the depletion of the organic substrate. All samples were naturally contaminated with microbiota. The dilutions contained brown soil dried and were rested at room temperature. The following proportions were used 1: 2n, i.e. 1:1, 1:16, 1:32, 1:64, 1:128. Four concentrations of brown soil (10 wt.%, 20 wt.%, 30 wt.% and 35 wt.%) were tested for only in sample No. P-O. After mixing with the drilling mud sample and hydration, the natural soil microbiota created the microbial inoculum and this was irrespective of the natural contamination of drilling fluids during the transport, disposal and in contact with microorganisms. All results are related to 1 g dry mass of drilling fluids or mixtures with soil. The respiratory quotient (RQ) was calculated from the ratio: RQ = CO2 produced / O2 consumed (1) where: the CO2 and O2 were to be given in the same units. The Penicillium sp. was determined based on conidiophore branching patterns observed under microscope in Penicillium according to Visagie et al. (Visagie et al. 2014).