Cheng Wang

[This corrects the article DOI: 10.1021/acsomega.2c07713.].

The integrated injection-production string is the core tool used in thermal recovery wells for heavy oil, the mechanical behavior of which is complex due to the coupling effect of downhole temperature and pressure and the load induced by steam huff and puff operations. In this paper, an analysis model that calculates the temperature and pressure field during steam huff and puff operations has been established based on the basic principles of energy conservation and heat transfer. Then, the force distribution and strength check of the integrated injection-production string were analyzed. The fatigue damage of the string was evaluated by considering dynamic loads during the injection process. The corrosion life of the string was predicted. Finally, the failure mechanism of the integrated injection-production string in thermal recovery wells for heavy oil was illustrated. The results showed that the strength of the string and vibration fatigue are not the main causes of failure, but corrosion is the main reason for string failure. The residual strength of the corroded string was greatly reduced, which is the fundamental reason for the failure of the string. This paper is of guiding significance to the optimization of design and safety evaluations of the integrated injection-production string in thermal recovery wells for heavy oil.

The composition of heavy oil is complex, and it is difficult to develop the heavy oil due to its high viscosity and poor fluidity. Therefore, it is very important to clarify the viscous mechanism of heavy oil. In this paper, typical ordinary heavy oil, extra heavy oil, and super heavy oil samples were selected to study the microstructure of heavy oil components and the mechanism of influence on viscosity of heavy oil. The molecular weight, element composition, and polarity of each SARA (short for Saturates, Aromatics, Resins and Asphaltene) component of heavy oil samples were measured and analyzed. The viscosity of heavy oil increases with the increase of the aggregate contents of resins and asphaltene. Resins and asphaltene in heavy oil have a high polarity, high heteroatomic content, and complex molecular structure, which are the key factors affecting the viscosity of heavy oil. On the basis of the experimental results, through simulation calculation and modeling, the microstructure and molecular formula of each component of different heavy oils are obtained, which provides a quantitative reference for revealing the viscosity mechanism of heavy oil. There is little difference in the elemental composition of resins and asphaltene, but the structure is very different and the difference in structure is the key factor leading to the difference in the properties of resins and asphaltene. The content and structure of resins and asphaltene in heavy oil are the key factors leading to the big difference in viscosity of heavy oils.

Oily sludge is a significant hazardous waste generated in the petroleum industry, and oily sludge reinjection and plugging is a new treatment technology developed in recent years, which is to reinjection oily sludge into the reservoir to plug channeling and improve the distribution of displacement front (profile conformance). However, there are many problems during oily sludge injection, such as high injection pressure or pump-block, due to the complex composition and poor suspension of oily sludge. Therefore, this paper proposes a dispersed oily sludge system, which can improve the stability and injectivity of the oily sludge by adding appropriate dispersants. The dispersants, a kind of interfacial active agent with strong lipophilicity and hydrophilicity, can greatly reduce the solid particle size and greatly improve the stability of the oily sludge by demulsifying the W/O emulsion and dispersing the solid particles. Through experiments, the optimal dispersant for oily sludge produced in Liaohe oilfield is AA/AMPS (Acrylic Acid and 2-Acrylamido-2-Methylpropane Sulfonic Acid Copolymer), and the optimal concentration of AA/AMPS is 1wt %. The oily sludge plugging experiments indicate that the raw and dispersed oily sludge have strong plugging ability, with the plugging rate exceeding 90% for the sandpack with permeability of 10000 mD. The dispersed oily sludge can greatly improve the injectivity of oily sludge, reduce the accidents in the injection process, and realize deep profile control, which is a potential in-situ treatment and application technology of oily sludge.

A modular multiple thermal fluid generator is introduced to enhance heavy oil production, which consists of water treatment system, fuel injection system, air compressor, central burning and heat exchanging system, and measuring and controlling system. All the components are mounted in three separated light shelters, which are easy to be lifted and installed, especially on the offshore production platform. It could be operated under 350 ℃ and 20 MPa, and the temperature and GWR (ratio of the volume of gas to the equivalent water volume of steam under standard conditions) could be adjusted by the water injection rate under the given heating capability of the central burning chamber. The temperature of the generated fluid is usually 200–300 ℃ with GWR of 200–300 m³/m³. Compared to conventional steam generator, such compact multiple thermal fluid generator is easy to be installed on the offshore oil production platform, and the generated multiple thermal fluid is potential to enhance heavy oil production in mechanisms of reducing heavy oil viscosity by both heating and injected gas, enlarging the heating reservoir chamber, and pressure by injected gas. In the past 10 years, the multiple thermal fluid generator has been applied to more than 40 wells in Bohai Offshore Oilfield and Xinjiang Oilfield in cyclic multiple thermal fluid stimulation (CMTFS in short) process. As a result, the multiple thermal fluid generators were operated soundly, and the heavy oil production of these wells was enhanced remarkably. (The oil production rate was 2–3 times more than cold production.)

Weak gel is a kind of three-dimensional cross-linking system with low polymer concentration and appropriate cross-linking agents, dominated by intermolecular cross-linking, supplemented by intramolecular cross-linking, and with a weak cross-linking degree. In this paper, the microstructure and properties of the weak gel were observed and evaluated under different conditions. Seepage behavior experiments and parallel core displacement experiments were carried out to evaluate profile control and flooding performance of the weak gel. Under a certain polymer concentration, with the increase in cross-linker concentration, the reticular structure of the weak gel becomes more uniform and the strength of the weak gel was further enhanced. Weak gel has more retention in porous media and greater strength. The profile control and flooding performance of the weak gel are much better than those of the polymer. A field test of weak-gel flooding was successfully carried out in LD10-1 oilfield. Most of the production wells around the weak gel injection wells responded after weak-gel injection and the accumulative oil incremental oil production of the test area was 57.8 × 10⁴ m³ up to December 2018.