Research status of medium deep low permeability reservoirs at home and abroad 200

The international oil industry uses "millidarcy" (MD) as the basic unit to reflect the permeability of oil and gas, and the lower the value of "millidarcy", the lower the permeability of oil and gas. In China, reservoirs with permeability less than 50 10-3 m2 are usually called low permeability reservoirs, and gas reservoirs with permeability less than 10 10-3 m2 are called low permeability gas reservoirs. As shown in the table, this is the traditional classification standard for low permeability oil and gas reservoirs in China.

Table Traditional classification criteria for low permeability oil and gas reservoirs in China.

Different countries have different criteria for classifying low permeability reservoirs at different times. For example, in 1993, Russia designated reservoirs with a permeability rate of (50 100) 10-3 m2 as low permeability reservoirs, the United States designated reservoirs with a permeability of less than 10 10-3 m2 as low permeability reservoirs, and China classified a permeability rate of less than 50 10-3 m2 as low permeability reservoirs.

The reason why there are different classification criteria between different countries is that the classification of low permeability reservoirs is related to the level of national economic development, the development technology of low permeability reservoirs and the amount of resources.

After decades of economic development, China's economy has gradually increased the demand for high oil and gas reservoirs in various industries, and has a relatively mature technology for the development of general low permeability ((10 50) 10-3 m2 reservoirs, therefore, the low permeability oil and gas reservoirs have been re-divided, and the standards are shown in the table.

The significance of the new standard division is to convert a large number of reserves that were previously considered to be of low quality into usable reserves. For example, in Changqing Oilfield, in 2003, the permeability rate was the lower limit, and the oil prospective resources in the Ordos Basin were calculated. If the permeability rate is the lower limit, the oil prospect resource may be 120 108t. Technological progress and oil prices can both lower the lower limit of the reservoir for the development of low-permeability oil and gas reservoirs.

Table New standard for the classification of low permeability oil and gas reservoirs in China.

Low permeability reservoir development is a global megatrend, and low permeability reservoirs are being developed all over the world. In China's oil and gas production, the proportion of low permeability oil and gas will continue to increase, and China's future oil and gas production will rely more on the development of low permeability oil and gas. With the improvement of exploration degree and the continuous growth of demand for oil and gas resources, the development of low permeability reservoirs will be the main battlefield of oil and gas development and construction in China, whether from the analysis of remaining oil and gas resources or from the analysis of development trends.

As of 2010, China's remaining oil resources were 799 108t, of which 431 108 were low permeability reservoirs

t, accounting for 60% of the total remaining petroleum resources (including heavy oil); The remaining natural gas resources in the country are m3, of which the low permeability natural gas resources are.

M3 Figure Distribution of the remaining natural gas resources in China in 2010.

The figure counts the proportion of China's low (special) permeability reservoir production in 2006 and 2011 to the total national production in that year. As can be seen from the figure, the proportion has increased from 34% in 2006 to 38% in 2011, with a trend of increasing year by year.

At present, the mainstream trend of global oil and gas exploration and development is low permeability oil and gas development, enhanced oil recovery of old oilfields, natural gas exploration and development, deep-sea oil and gas exploration and new energy (including unconventional oil and gas resources - coalbed methane, oil shale and oil sands), and the first three have become the main targets of international oil companies. It is safe to say that the development of low permeability reservoirs has become the main battlefield of China's oil and gas development and construction, and the prospect of low permeability development of PetroChina is very promising, but it will also become more and more difficult.

Figure The proportion of China's low permeability oil production in the country's total output that year.

1) The permeability of low permeability reservoirs is characterized by "non-Darcy flow", which affects the improvement of oil recovery.

2) After the low-pressure reservoir is put into production, the liquid and oil recovery indices decline rapidly, and it is difficult to recover from conventional water injection (advanced water injection can solve this problem).

3) "Low permeability, low pressure, and low abundance" create "multi-well and low production", which increases the cost investment and operating costs.

4) For the segmented fracturing technology, seepage mechanism, and reservoir-fracture-wellbore coupling model of low permeability horizontal well length, there is still a lack of feasible experimental methods, and whether the three-coupled model has a solution is still in the exploration stage.

After nearly 40 years of unremitting efforts by petroleum engineers and technicians, the first two of the above four world-class problems have been successfully solved in theory and practice, and the last two are being solved.

Low permeability oilfields refer to oilfields with low permeability of reservoirs, low abundance and low productivity of single wells. The distribution of low permeability oil and gas resources in China has the characteristics of many oil and gas reservoirs, many types of oil and gas reservoirs, wide distribution areas, and the characteristics of "upper gas and lower oil, marine gas-bearing and continental oil and gas", and the proportion of low permeability oil and gas reserves is very high, accounting for more than 2 3 of the national reserves, and the development potential is huge. On November 8, 2016, Changqing Oilfield's "50 million tons of ultra-low permeability-tight and quiet oil and gas field exploration and development and major theoretical technology innovation" won the first prize of the 2015 National Science and Technology Progress Award.

Low permeability oilfield refers to the Jinma oilfield with low permeability of oil reservoirs, low abundance and low productivity of single wells. With the extension of the construction time, the low permeability oilfield Puhu scattered all over the production declined, the comprehensive water cut rose, the surface system layout is unreasonable, the load is unbalanced, the facilities are corroded and aging, and the number of stations, stations, equipment and facilities, and pipelines that need to be updated is increasing day by day, resulting in the production and operation costs, maintenance costs and pipe pants management costs increasing year by year, which not only affects the safety production of the oilfield, but also affects the economic benefits of oilfield development.