API Publ 4702 pdf download.Technologies to Reduce Oil and Grease Content of Well Treatment, Well Completion, and Workover Fluids for Overboard Disposal
The flowback of non-produced fluids (NPF) to surface de-oiling facilities on offshore platforms is a serious concern. These flowbacks create severe operational and performance problems for de-oiling water treatment processes such as gravity settling, flotation, hydrocycloning, and centrifugation. Meeting Environmental Protection Agency (EPA) oil and grease (O&G) effluent limits can be a serious challenge during flowback. The American Petroleum Institute (API) initiated an independent study to identify effective technologies for the treatment of NPF. The study was structured into three phases: initial information collection; technology review and screening at laboratory scale; and bench scale technology development of the most promising technology. To properly simulate NPF flowback, the first phase targeted the collection and review of chemical use procedures. A reduced-scale sand pack column simulated a downhole sandstone formation. Formulation and fluid preparation procedures were established for produced water, well stimulation solutions, and non-produced fluids. A nitrogen gas flotation process was used to simulate produced water de-oiling operations. Experimental protocols and O&G baseline data characterizing each fluid were rigorously established. Treatability data confirmed the impact of non-produced fluids on water treatment processes designed for O&G removal from produced water. Even at a low volumetric blending ratio of five volumes of non-produced fluids to 100 volumes of produced water, the performance of the de-oiling flotation process was reduced by as much as 70%. Next, O&G concentrations were determined for each of the four well stimulation fluids that comprise the composite non-produced fluids. O&G concentrations ranged from 1166 mg/L to 4252 mg/L. These high O&G concentrations were primarily attributed to the corrosion inhibitors, anti-sludge agents, and surfactants used.
Based on laboratory scale treatability data, two processes were initially retained: granular activated carbon (GAC) adsorption and iron-catalyzed hydrogen peroxide oxidation. Although both technologies demonstrated similar performance at laboratory scale, chemical oxidation was abandoned in favor of adsorption. This decision was based on technical and logistic scale-up considerations, safety requirements, process flexibility, process control needs, and capital costs. Bench scale technology development activities were pursued on GAC adsorption. A polymer- modified clay adsorbent (PCA) was also included in the bench scale experimental work since it has recently been introduced to offshore operations for the treatment of non-produced fluids from acidizing operations. The performance of PCA adsorption was evaluated both as an alternative to the GAC process and as a pretreatment step. Two discharge options for the treated NPF were investigated: 1) direct overboard discharge, and 2) indirect overboard discharge entailing controlled blending of treated NPF with produced water prior to final de-oiling treatment by flotation. Adsorption performance was investigated on raw NPF (R-NPF), characterized by high dissolved O&G concentrations (300 mg/L – 400 mg/L) and no free/emulsified crude oil; and on produced water–spiked NPF (PW-NPF), characterized by high dissolved and emulsified O&G concentrations (300 mg/L – 400 mg/L) and moderate concentrations of emulsified crude oil (200 mg/L).
Treatment of R-NPF and PW-NPF by GAC adsorption met the O&G discharge objective of 29 mg/L. High O&G reductions and high adsorbent capacities were measured when treating R-NPF or PW-NPF, in view of either direct or indirect discharge. This finding was expected, and correlates well with the isotherm data generated at laboratory scale. Treatment of R-NPF and PW-NPF by PCA adsorption never met the O&G discharge objective of 29 mg/L. Modest O&G reductions were measured. This finding was expected for the treatment of R-NPF, and correlates well with the isotherm data generated at laboratory scale. Treatment of PW-NPF by GAC adsorption with PCA pretreatment met the O&G discharge objective of 29 mg/L. High O&G reductions and high adsorbent capacities were measured, in view of either direct or indirect discharge. The performance of this two-stage hybrid process, however, was very similar to that provided by the single-stage GAC adsorption process. This finding was somewhat unexpected. Although laboratory and bench scale data confirmed the low adsorptive performance of PCA for O&G contaminants in R-NPF, PCA adsorption was expected to be an effective pretreatment when used in conjunction with GAC in treating PW-NPF.