Future Trends for Tight Oil Exploitation

Abstract

In this paper, production characteristics of tight oil reservoirs are summarized and analyzed, the investigated reservoirs include Cardium sandstone reservoir and Pekisko limestone reservoir. The phenomenon that gas and oil or water and oil are co-produced at an early stage of exploitation has been observed. In addition, water cut of many tight oil producers remains constant or undergoes reduction as production proceeds within first 36 months. Since an oil rate drops quite a lot in the first year's production of tight oil reservoirs, reservoir simulations are run to investigate an effect of different parameters on tight oil production. Randomized experiments are created with geological and engineering parameters as uncertain factors and an oil rate as the response factor. The method of analysis of variance (ANOVA) is used to analyze the difference between group means and to determine statistical significance. Reservoir properties such as permeability, pressure, wettability, oil API, and oil saturation and engineering parameters including a fracture stage and well operations have tremendous effects on oil production. Oil recovery factor increment in tight oil reservoirs highly depends on enlarging a contact area, improving oil relative permeability, reducing oil viscosity and altering wettability. Future research and development trends in tight oil exploitation are highlighted. As primary recovery is quite low in tight oil reservoirs, the multistage fracturing technology is a necessity and it must be conducted based on a deep understanding of petrophysical and geomechanical properties. Water alternating gas (WAG) seems the best fit for tight oil exploitation. The way to improve WAG performance, including CO2 foam stabilized with surfactant or nanoparticles, low salinity water or nanofluids alternating CO2, will earn more and more attention in the future of tight oil development.

Accumulation Conditions and Pattern of Tight Oil in the Lower Submember of the Fourth Member of the Shahejie Formation in the Damintun Sag, Bohai Bay Basin

“…Tight oil refers to the oil accumulated in or immediately adjacent to the tight reservoirs in high-quality oil source strata without experiencing long-distance migration on a large scale. It is an unconventional oil resource, whose reservoirs have low porosity and low permeability [1][2][3][4][5][6][7]. Compared with other reservoirs with particularly low or ultra-low permeability, tight oil resources have more complicated accumulation mechanisms, finer pore throats, and higher interstitial material content and thus are more difficult to explore.…”

Study on the Imbibition Characteristics of Different Types of Pore-Throat Based on Nuclear Magnetic Resonance Technology

“…The development potential of low-permeability tight oil reservoirs is huge [1,2], and imbibition oil recovery has become the most effective method for enhancing oil recovery for this type of oil reservoirs [3,4]. Its principle is to use capillary force as the main displacement power to enhance the oilwater replacement capacity between fractures and rock matrix [5,6].…”

Imbibition and Oil Recovery Mechanism of Fracturing Fluids in Tight Sandstone Reservoirs

“… 3 Imbibition is an important development method for tight sandstone reservoirs. 4 − 7 Tight oil production from reservoirs highly depends on the spontaneous imbibition of tight rocks. 8 , 9 Spontaneous imbibition and forced imbibition are two different imbibition categories, depending on whether the injected water is imbibed by capillary pressure alone or by other forces.…”

“…Spontaneous imbibition is defined as the imbibed process of water into rocks at different reservoir conditions . Imbibition is an important development method for tight sandstone reservoirs. − Tight oil production from reservoirs highly depends on the spontaneous imbibition of tight rocks. , Spontaneous imbibition and forced imbibition are two different imbibition categories, depending on whether the injected water is imbibed by capillary pressure alone or by other forces. Spontaneous imbibition dominates the entire oil displacement process. , The capillary pressure between water and in situ crude oil is the primary mechanism for controlling oil production from fractured tight reservoirs .…”