Research on the stimulation technology for ultra-deep tuff reservoirs modification in northeast Sichuan
Author of the article:LIU Hu1, ZUO Luo2,3, YIN Decan1, JIANG Tingxue2,3, DUAN Hua1, WANG Haitao2,3
Author's Workplace:1. Sinopec Exploration Company, Chengdu, Sichuan, 610041, China; 2. State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Effective Development, Beijing, 102206, China; 3. Sinopec Research Institute of Petroleum Engineering Co., Ltd., Beijing, 102206, China
Key Words:Ultra-deep;Tuff; Acidification; Acid fracturing; Carbon dioxide
Abstract:
Reservoir
stimulation technology of horizontal wells in ultra-deep tuff reservoirs in northeastern Sichuan is not
well established, then, analyzing geological characteristics, testing of
physical parameters and rock mechanics parameters, and the research on the
characteristics of fracture initiation and expansion are carried out to explore
its effect on reservoir stimulation. The study shows that the ultra-deep tuff reservoir in northeastern Sichuan is thin
in thickness, and belongs to low porosity and low permeability reservoir,
featuring high clay mineral content, low brittleness index, strong plasticity,
and complex lithology in the vertical direction of stratum; the fracture
pressure of the reservoir is above 170 MPa, the stress difference is greater
than 20 MPa, the fracture initiation and expansion are difficult, and at the
same time, it is easy to cause high pumping pressure; as stratum is easy to
disperse and collapse after the action of the reservoir rock and the acid
system, so staged acid fracturing completion mode with cementing slip casing is
mostly needed, which all need to be equipped with 175 MPa fracturing wellhead
and equipment to enhance pumping rate and fracturing effect; measures such as
pre-padding liquid CO2 and
low-viscosity liquid,
using deep penetration with aperture perforation and high-temperature resistant heavier fracturing fluid can
lower the fracturing pressure and pumping pressure; it is recommended to use
15% hydrochloric acid as the base liquid of the acid fluid system. The acid
fluid system must meet the requirements of 160℃rheological test and 140℃dynamic corrosion and no weak crosslinking and viscosity increase
after standing for 7 days, and viscosity reaches 40 mPa·s and above after shearing for 35 min, as well less residue, no
precipitation and no agglomeration. The stimulation technology for reservoir
modification proposed in this paper is important reference and guidance for the
effective exploration and development of ultra-deep tuff reservoirs in northeast Sichuan in the
future.