Ma, Yingxian (Southwest Petroleum University) | Ma, Leyao (Southwest Petroleum University) | Guo, Jianchun (Southwest Petroleum University) | Lai, Jie (Southwest Petroleum University) | Zhou, Han (Downhole Service Company, CNPC Chuanqing Drilling Engineering Company Limited) | Li, Jia (Downhole Service Company, CNPC Chuanqing Drilling Engineering Company Limited)
We prepared physically linked allyl alcohol polymer/polyacrylamide double network hydrogels via onepot strategy. These double network supermolecular fracturing fluids were found to have a better viscosity at high temperature compared to the conventional polyacrylamide systems. After testing with a rheometer, the fluid viscosity could stay 320 mPa s at 150 C under 170/s shear rate. With NMR and FT-IR results' help, we determined that abundant polar groups of chains were still free, which could complex ions to keep, even enhance the chain stability. Thus, these double network systems showed excellent salt resistance with the non-covalent interactions and physical entanglements, and the viscosity of the allyl alcohol polymer/ polyacrylamide system did not drop but increase. The viscosity in high salinity could increase nearly 40 % compared with the initial situation. Overall, the novel fracturing fluid system could maintain a high viscosity and better rheological properties under high salinity and showed excellent high-temperature stability, to make up the lack of fracturing fluid at this stage. It is expected to potential fluid issues caused by low water quality and harsh downhole temperatures were resolved or mitigated.
The formation of silica and silicate scales caused troublesome issues in various water-handling systems, including steam generators, geothermal wells, and waste-water disposal systems. Recently, a produced water with over 300 ppm of silica, and a spent brine off the strong acid cation (SAC) softeners containing high levels of calcium (Ca), barium (Ba), and magnesium (Mg) were commingled in the production wells. The mixing of these two waters induced silicate as well as other scales, including calcite, barite, etc. In order to provide effective scale inhibition when these waters are mixed, effective scale inhibitors for both silicate and other scales were requested for evaluation.
In this paper, scale inhibitor chemistries for preventing both silica/silicate and other scales were reviewed and the possible synergistic effects were assessed by Design of Experiment (DOE) software. DOE is a systematic method to determine the relationship between several factors, i.e. various chemistries and the performance of formulations under designed application conditions. Selected chemicals were formulated for control of both silica/silicates and other scales, and their performances were evaluated by a Kinetic Turbidity Test (KTT). The KTT is a novel laboratory test method using an Ultraviolet-Visible (UV-Vis) spectrophotometer to monitor the formation of scales at various dosages of tested products. Bottle tests were also conducted for the comparison of inhibition performance.
Based on the lab testing results from the KTT and the bottle tests, the combined products exhibited good scale inhibition performance for both silicate and other scales. The product was recommended for field applications. Subsequent field applications of this product have provided the desired scale control.
This paper presents the laboratory testing data for scale inhibitor selection for the combination products on both silica/silicate control and other scale control by using the efficient performance evaluation method. It also provides an effective product formulation approach for finding synergetic effects of different products. Successful scale inhibitor implementations in the field applications are also presented in this paper. Both laboratory and field testing results show a good case history for the optimization of the silica/silicate and other scale treatment.
When produced water from offshore production is discharged to sea, it contains some oil (aliphatic and aromatic components), production chemicals and NORM (Naturally Occurring Radioactive Substances). These groups of substances are traditionally treated in different ways in the regulations and standards.
Regulations of oil in produced water are mainly related to max concentrations and the total discharge of the aliphatic (dispersed) fraction. Regulation of chemicals is based on the environmental risk profile of each production chemical, although efforts are made towards regulations based on risk assessment of the discharge of the mixture of substances. For discharge of NORM dissolved in the produced water, no limit values are imposed. For NORM solids (scale, sludge, sand) from process equipment, discharge to sea is in general not allowed - it is re-injected or taken to a deposit onshore.
Management of safety risks takes place based on the principle that risks shall be reduced to a level As Low As Reasonably Practicable (ALARP). The concept of environmental risk is not as unambiguously defined as safety risks. With respect to accidental environmental impacts, the parallel is relatively straightforward, but with respect to planned environmental impacts (e.g. emissions/discharges during operation) the parallel to the safety ALARP is not so clear; the consequence (the environmental impact) is not linked to a certain frequency - i.e. we cannot talk about risk as: likelihood times consequence.
Costs are normally defined as money, effort and time. But what if the cost of a reduced HSE risk is an increase in another HSE risk? Produced water re-injection might cause increased CO2 emissions. Handling solid NORM when shipping it to shore causes health risks to the people handling the NORM. Can that risk be justified, based on the possible reduction in environmental risk by not discharging the solid NORM to sea instead?
The paper highlights the above issues and proposes a method named integrated HSE ALARP assessment for supporting such analysis. The environmental risks of discharge with produced water to sea of oil, chemicals and NORM, respectively, are used to illustrate these principles.
The development of the concept of risk has previously taken place with respect to safety risk. An important principle developed is the obligation to reduce risk to a level As Low As Reasonably Practicable (ALARP). The concepts of health risk and environmental risk are also widely used now - and as parallel to the ALARP principle, the principles of Best Available Technology / Best Environmental Practice (BAT / BEP) has been developed with respect to environmental impacts. These principles are to a wide extent analogous to the ALARP principle used in health & safety.
In this paper, an overall common definition of HSE risk is sought. This makes weighting of different HSE risks against each other more transparent and objective. The ALARP principle traditionally weight safety risk reduction against the increased cost/effort required for achieving the risk reduction. In this paper, a concept for weighting safety risk against environmental and health risk is presented, using produced water as an example. Also a situation where increased environmental impact was weighted against reduced safety risk is presented.
IPTC 10911 How Clean is Clean? Is It Still a Debate? Copyright 2005, International Petroleum Technology Conference This paper was prepared for presentation at the International Petroleum Technology Conference held in Doha, Qatar, 21-23 November 2005. This paper was selected for presentation by an IPTC Programme Committee following review of information contained in an proposal submitted by the author(s). Contents of the paper, as presented, have not been reviewed by the International Petroleum Technology Conference and are subject to correction by the author(s). The material, as presented, does not necessarily reflect any position of the International Petroleum Technology Conference, its officers, or members. Papers presented at IPTC are subject to publication review by Sponsor Society Committees of IPTC. Electronic reproduction, distribution, or storage of any part of this paper for commercial purposes without the written consent of the International Petroleum Technology Conference is prohibited.