Feasibility Study On Acidic Pressure Modification Of High Calcareous Dense Oil Reservoir

The Junggar Basin in the Early-Mid Permian is a saline lacustrine basin, where a set of hybrid sedimentation of sandstone and dolomitic rock is developed. Exploration proved that it is a continuous reservoir of self-generation and self-storage and provides good conditions for tight oils accumulation of proximal source type. Therefore it is a typical tight oil characteristics and also difficult to be developed. Tight oil reservoir belongs to extra-low porosity and permeability oilfield with lower production naturally. All oil wells completed in tight reservoirs require facture stimulation to achieve commercial production and improve well productivity. Different technologies are used for different plays but the most common methods used today are vertical or horizontal drilling and multi-stage hydraulic fracturing. However, whether or not the technique could maximize the efficiency and further improve the technique and enhance the tight oil production after fracturing? In allusion to the problems above, the past ideas for reservoir reconstruction were changed, for the existence of calcareous and siliceous cements in tight oil reservoirs, acidizing or composite fracturing with acid fracturing and sand fracturing were studied. Experiments on acid system optimization, acid-rock reaction and acid etched fracture conductivity were conducted, a new technique of composite fracturing was proposed. The thesis mainly achieves the following content:Firstly, fracability is the capability of the stone that can be fractured effectively during hydraulic fracturing. Shale brittleness, brittle mineral content, nature fracture and diagenesis are mainly influencing factors of shale fracability. A mathematical model is established to quantitatively evaluate the tight oil reservoir fracability.Secondly, an experimental method of acid rock reaction kinetics was set up to get the reaction equation between acid and tight oil reservoir. The result was compared carbonate reservoir with tight oil reservoir. The factors affecting reaction rate of acid type, reaction temperature, and acid concentration were systematically analyzed.Thirdly, the adaptability of several major acid systems and acid fracturing technologies for tight oil reservoir have been accessed based on acid rock conductivity experiments, then the type of acid and acid fracturing technology which aim at tight oil reservoirs with high calcium content.Fourth, a new technique combined fracturing with acidizing and sand fracturing was proposed. Both experiment and simulation indicate that this new technique superior to conventional fracturing.Finally, Considering the character, mineralogical and cementation type of tight oli formation, the tight oil formation can apply acid fracturing by optimizing acidizing fluid type and concentration if the HCl dissolvability is high and cementation is fine. However, if the HCl dissolvability is high and cementation is relatively low, I recommend applying a new technique combined fracturing with acidizing and sand fracturing.In this paper, the results achieved by a series of studies to explore the tight oil reservoir acid fracturing feasibility, expanded the idea of tight oil reservoir stimulation, the results of the paper can serve as guidance for the stimulation treatment of tight oil reservoir with high calcium content. Also, this work can help operators to perform treatments to enhance recovery in other unconventional oil reservoirs with high calcium content.