Cyclic steam simulation (CSS) was widely used to recover heavy oil in shallow reservoirs in Kazakhstan. In the late stage of CSS in M oilfield, the performance of this CSS project was poor with high water cut and low oil steam ratio (OSR), indicating low economic benefit. The multi-component thermal fluid (MTF) stimulation trial has been conducted there since March 2018 to evaluate the feasibility of this technology. This paper introduces the field experience and the production performance of MTF stimulation. Results are from 32 cycles of MTF stimulations in 23 wells, most of which had completed their 4 cycles of CSS before. MTF technology is based on a high-pressure jet combustion mechanism, generating a mixture of nitrogen, carbon dioxide and vapor (MTF) under a sealed combustion condition. The mixture fluid provides a significant enhancement through a synergistic effect in the reservoir. The soaking and recovery process are the same as the conventional steam stimulation, meanwhile the requirements for completion and wellbore structure are the same as well. By the time of statistic, average cyclic OSR reaches 2.19 from 0.49 of last CSS cycle. Average water cut declines from 90% to 40% and daily oil production rises from 22 bbls to 33 bbls. Free water is almost invisible in the produced fluid, instead, a stable quasi-monophasic flow has been presented even at low temperatures. This effectively increases the fluidity and dilatancy of crude oil, and greatly replenishes the elastic energy of the formation. Meanwhile, with all components injected into the formation, MTF stimulation achieves significant reduction in carbon emissions. Although this is a pilot test, considerable economic benefits have been achieved with the increase of oil production efficiency. MTF stimulation brings an additional profit of USD 4.4 million for the first year under conditions of local material's cost. This successful pilot demonstrates that MTF stimulation may play an important role at late stage of CSS, even it has its own prospect in an initial heavy oil reservoir development. In the meantime, this pilot experience can be used as a reference for other similar reservoirs’ development.

Heavy oil reservoirs are generally unconsolidated and easy to produce sand during production1. In the late stage of Cyclic Steam Stimulation (CSS), high temperature steam and hot water destroy clay minerals, further aggravate sand production problems, resulting in sand jam, sand burial, pump jam and casing damage, and frequent operations seriously affect the effective production of oil wells. PetroChina has been carrying out steam stimulation for more than 40 years, and has formed a series of sand control technologies in the field of heavy oil thermal recovery. This paper introduces several sand control techniques used in Liaohe and Xinjiang Oilfield and their successful cases. Liaohe and Xinjiang Oilfield is rich in heavy oil resources. The oil types include ordinary heavy oil, extra heavy oil and super heavy oil2. In Liaohe Oilfield, they have medium and deep heavy oil with a depth of 600-900m and super deep heavy oil with a depth of 1300-1700m. As the main development method, CSS has entered the late stage of production, more than 9 cycles, and encountered various sanding problems during the production. By using mechanical sand control and chemical sand control measures, the sand path was controlled, and an artificial wellbore was formed in the near-wellbore zone to control the fine silt. Through the discussion in this paper, we can provide a variety of solutions for sanding problems encountered in heavy oil steam handling.

North Buzachi field is structurally located in the western part of Ustyurt Basin on the edge of Caspian Sea in Kazakhstan. It's a heavy oil reservoir with viscosity nearly 400 mPa·s at 33°C. After nearly 20 years of cold-water flooding, the oil production has fallen sharply. Low sweep efficiency and high water cut come to be the main severe challenges at this stage. Ways to improve efficiency and productivity need to be tried and evaluated. Water shut off tests, polymer flooding and adjusting perforations have been tried, but with little success. Thermal enhanced oil recovery (EOR) methods generally are effective options and cyclic steam stimulation (CSS) was considered. But the high-water saturation and water cut make CSS get rapid economic decline after 1 or 2 cycle. Therefore, the feasibility of Gas-Steam Composite Stimulation (GSCS) on this field is studied and evaluated. This paper shows the prospect of GSCS in this reservoir by studying flow mechanisms and numerical simulation analysis. Gas-Steam Composite is a mixture of steam, carbon dioxide and nitrogen, which is produced based on a high-pressure jet combustion mechanism. The mixed components are simultaneously injected into the formation at the same pressure and temperature. GSCS has been tried in other similar oil fields (Mortuk oil field in Kazakhstan) before, and the actual production results are better than predicted. The application prediction of North Buzachi field was based on the previous theory and experience. During the GSCS progress, gas overlap occurs underground, resulting in secondary gas cap drive and higher reservoir pressure. Along with other synergistic effects, the oil rate can theoretically increase to 4-5 times of water flooding in North Buzachi field. By the results of numerical simulation, the upper residual oil was swept and the sweep efficiency increase from 14% to 40%. The daily oil production per well grows from the initial 3.5 t/d to 15 t/d. Compared with the final recovery of 12% by water flooding, the recovery may reach 33.4% after 7 cycles of GSCS. Meanwhile, the water cut declines from 97% to 50% and the average cyclic oil-steam ratio reaches 4.24. Economical evaluation shows that cost per ton of oil can be reduced by 24%. With the remarkable increase in production, more economic benefits can be achieved with GSCS technology. This study not only lays the groundwork for future pilot of GSCS in this field, but also provides a significant reference for the development of similar heavy oil reservoirs.