Essay Example on Deep-Water Wax Deposition: Challenges & Solutions

Increased exploration of deep-water fields prompts the need to understand the mechanisms of wax deposition and the available methods for its prevention and remediation within production and export systems. There are serious production and transportation challenges resulting from asphaltenes deposits that consist of resins and foreign particles that clog flowlines and tubing. Addressing this challenge comes at a great cost. Wax deposition in cold-environment hydrocarbon tubing is a major challenge for oil engineers as it impedes flow assurance. Such challenges are characterized by reduced crude oil flow, pressure abnormalities, and artificial blockages. Flow assurance guarantees the transportation of fluid from its reservoir to process installations and is an extremely vital part of the oil and gas industry.

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Wellbore and flowlines suffer blockages that lead to various production problems. These blockages are the result of high molecular alkane deposits. Paraffins are high molecular alkanes made up of more than 20 carbon atoms and contribute these deposits. The increased thickness of these deposits leads to a gradual decline in production. The depositions increase the surface roughness of flow pipes and valves and cause various instrumentation challenged. These deposits vary in consistency from soft accumulations to hard brittle deposits. Usually, the deposits become firmer and harder with an increased molecular weight of the paraffin deposits. Several remedial actions are needed to address this flow challenge.

Flow stability is a necessary yet costly undertaking in the petroleum industry. Several factors, including organic and inorganic depositions, gas hydrates that form from water, and hydrocarbon mixing create conditions that have a great economic impact on oil and gas companies. Wax deposition refers to the growth of the final solid layer on the surface, which eventually attaches itself to the crude oil. Several factors accelerate the deposition. Temperature is one of the leading catalysts of such deposition. A decrease in temperature results in a decline in the solubility of paraffin. It also leads to a temperature gradient that acts as a perfect condition for wax deposition. The pressure is another factor. An increase in pressure raises the solvent ratio and causes wax deposition. There is also a flow rate, whose decrease results in an increase in the wax deposition.

There is a need for remedial actions to avoid time and production loss resulting from wax deposition on flowlines. There are several techniques that are applicable to this end. Wax chemical inhibitors, coating materials, heat-proofing, and cold flow are some of these techniques. It is noteworthy, that if the wax is deposited after the previous remediation, then other techniques, such as mechanical method, may be used to remove the depositions. In this approach, a pig is driven through the pipe by a pressure differential. The design of these pigs allows them to push any loose material through the pipeline, and to ensure that a mechanical force results between the pig and the pipe wall, which effectively removes the debris. An alternative approach is a chemical method, in which wax solvents help to resolve the precipitated wax and ease the transportation of crude oil to the surface. In this method, solvents are applied in the frequent batch treatments or continuously. Aliphatic and aromatic solvents are the most applicable solvent groups in oilfields.

Besides these two approaches, the thermal technique may also be used for paraffin removal. In this approach, the hot oil is injected into pipes to melt the wax. The thermochemical approach involves wax treatment and is the most economically, controllably, and suitably advanced approach for most paraffin removal and remedial processes. In this technique, heat resulting from exothermic reactions is used to melt the wax deposits in flowlines or in the down-hole. The most appropriate remediation method is determined from the percentage of water cut in the oil and wax content. This report aims to look into the organic deposition of wax, its prevention using chemical wax inhibitors and chemical, mechanical, thermal, biological, and thermochemical treatment techniques.

The methodology of this study adds to the credibility of its findings and plays an instrumental role in its success. A mixed research methodology was determined as the most appropriate for assessing the best approach that is applicable to the prevention and mitigation of paraffin deposition in flowlines and tubing. The choice of a qualitative and qualitative approach that employs a case study was influenced by the need to achieve objectivity. An extensive data collection ensured that credible data on different approaches to the prevention of wax deposition in flowlines and tubing was gathered. A deviation from standard data collection approaches was necessitated by the scientific nature of the study. Hence, a more hands-on approach was employed. An experimental method was crucial for the assessment of the cause and effect attributed to paraffin deposition in flowlines and tubing, and the underlying phenomena. Notable demerits of the case study approach included an inability to assess the best method that could be executed first.

The study determined that, whereas there are several problems faced by oil wells, wax deposition is the most frequent. Wax forms when the temperature of the output fluid falls below the temperature of wax appearance, which often happens between 40 to 50 oC, and the temperature of pour point (42 to 44 oC). In this report, a case study is presented to establish the best method to eliminate wax deposition. A new means for the prevention of wax formation is proposed. The two methodologies provided in the study were first implemented in three Libyan oil wells. In the first method, the gas was injected at a 1208 psi pressure and 65 oC temperature, which was higher than the pour-point temperature. In the second technique, wax inhibitors consisting of trichloroethylene-xylene (TEX) were injected with gas inside the casing. The application of these new methods, it was determined from ground observations, promotes the cleanliness of production string, and eliminates wax. These methods were also useful for the prevention of wax formation.

Conclusion

Temperature, flow rate, pressure, and the mixing of suitable solvents are major causes of wax deposition. Paraffin wax that occurs in cold deep offshore fields results in many flow problems in the oil and gas industry. Almost all of the global oil exploration sites are affected by solidification and precipitation of paraffin wax that blocks the pores and fluid streams on the wells. The prevention of these production and transportation limitations requires the use of alternative approaches to paraffin wax prevention and elimination from flowlines and tubing. The methods preferred must be environmentally friendly, and cost-effective. The two methods determined in the study comply with this requirement. In the first approach, gas is injected at 86.3 bar and temperature raised above wax appearance temperature. The second approach requires the injection of chemical inhibitors along with the gas in the casing.