Research on the Enhanced Oil Recovery Technique of Horizontal Well Volume Fracturing and CO₂ Huff-n-Puff in Tight Oil Reservoirs

Abstract

The low oil productivity of tight oil reservoirs is mainly caused by poor reservoir physical properties such as low porosity and permeability, a small pore and throat ratio, and bad well connectivity, which lead to bad water injection capability and rapid pressure decline for the reservoir. In this paper, an enhanced oil recovery technique for tight oil reservoirs is proposed by combination of horizontal well volume fracturing and CO2 huff-n-puff to improve the reservoir physical properties and increase the flow capability of crude oil. In the initial reservoir development stage, the precise horizontal well trajectory and reservoir volume fracturing scale are designed by analyzing the distribution of sand body thickness and the oily sedimentary facies. The micro-seismic tracking technique is also used to monitor the fracture elongation. When the reservoir energy cannot satisfy the economic limit of oil productivity, the CO2 huff-n-puff technique is applied to increase the reservoir energy quickly. After the precise fracturing technique is used in tight oil Block X, the average oil production rate of six fractured horizontal wells increases by 5 ton (1 ton = 7.33 bbl) at the initial production stage, and the effective oil production increase life lasts for 32 months. When the reservoir energy is supplemented using the CO2 huff-n-puff technique, the oil production rate of pilot experiment well SP-1 increases from 1.9 to 12.8 ton with a cumulative oil increase of 1333.8 ton.

Study and Field Trials on Dissolvable Frac Plugs for Slightly Deformed Casing Horizontal Well Volume Fracturing

“…In zone III (>80 °C), the dissolution rate begins to accelerate and bubbles become obvious. (2) The dissolution rate of the magnesiumbased alloy in Cl − solution is higher than that in saline solution as a whole, which is in accordance with the dissolution mechanism of negative differential effect of magnesium-based alloys in Cl − solution, and the dissolution rate also accelerates with the increase of Cl − concentration or salinity, as shown in Figure 10.…”

“…In 2013, the application rate of “drillable frac plug and cluster perforation” volume fracturing in North America reached 85%. 2 Since 2010, new ideas of “volume fracturing” and “fracture-controlled reserves” transformation method have been implemented to form the “horizontal well casing completion and cluster perforation and frac plug section,” the body of the fracturing process. 3 However, with the increase of fracturing scale and well number, there would be more and more slight casing deformations in some well sections due to various reasons.…”

“…In 2009, more than 95% of wells were completed in unconventional gas horizontal wells in the United States. In 2013, the application rate of “drillable frac plug and cluster perforation” volume fracturing in North America reached 85% . Since 2010, new ideas of “volume fracturing” and “fracture-controlled reserves” transformation method have been implemented to form the “horizontal well casing completion and cluster perforation and frac plug section,” the body of the fracturing process .…”

Microscopic Production Characteristics of Pore Crude Oil and Influencing Factors during Enhanced Oil Recovery by Air Injection in Shale Oil Reservoirs

“…The small pores in the matrix correspond to a larger capillary pressure and a stronger seepage resistance. Therefore, after shale fracturing, the small-pore oil in the matrix tends to migrate to microfractures such as shale bedding fractures, while the oil collected in shale bedding fractures tends to migrate to strong support fractures; thus, microfractures such as bedding fractures can be regarded as bridges between the small pores of the matrix and the strong supporting fractures, which allows the crude oil to flow to the well casing and be produced. , In fact, when fractures are developed in shale cores, crude oil in fractures and macropores can be discharged in the early stage of air flooding, and the pressure difference sweep plays a major role . With the increase of air injection volume, the pressure will be transmitted to the small pores in the matrix, and the dissolution sweep will contribute more to the production of crude oil; hence, the recovery greatly increased.…”

Oil Production Mechanism of Water Injection Huff-n-Puff for Enhancing Oil Recovery in Tight Sandstone Reservoir

“…15,16 Bai proposed an enhanced oil recovery technology by the combination of horizontal well volume fracturing and CO 2 huff-n-puff, which was successfully applied to six fractured horizontal wells and achieved good oil increase effect. 15 Pu conducted hydraulic fracturing and carbon dioxide huff-n-puff experiments using a true triaxial stress core fracturing and displacement system. 17 However, high-pressure CO 2 injection has its limitations, such as the shortage of CO 2 , channeling problems during the high-pressure gases injection process, higher cost, and more challenging logistics than the use of water or water-based solution EOR.…”