Page 224 - Gas Wettability of Reservoir Rock Surfaces with Porous Media

208 Gas Wettability of Reservoir Rock Surfaces with Porous Media

6.1.5 Field Applications
The fault block Chang 68 at Weibei oil-gas field was considered as a sample,
with the aim to improve the properties of rock surfaces using drilling comple-
tion fluid system that protect low-permeability and extra-low-permeability
reservoirs.
The difference of clay mineral and illite-montmorillonite mixed-layers con-
tained in the fault block layer and reservoirs of Chang 68 at Weibei oil-gas
field is great, and reservoir water salinity (30,000 mg/L around) is high
belonging to low-pore and with extra-low-permeability reservoirs. The pore
size is small (the maximum pore-throat size is 0.494B1.4835 μm), making it
medium to strongly water sensitive, acid sensitive, and a medium salt sensitive
reservoir. The critical salinity level is 30,000 mg/L. The potential damaging
factors to reservoirs mainly include clay hydration expansion, dispersion,
water-blocks, and inorganic scale damage. Thus, compact mud cake is required
on well walls effectively to block the filtrate of drilling completion fluids from
entering the reservoirs, when the drilling completion fluid system is designed.
At the same time, intrusion reservoir fluid should have the properties such as
a low interfacial tension, avoiding water lock damage, conducing to the
flowback, and reducing reservoir damage. With improvements in the upper
drilling fluid, there are improvements in the properties of rock surfaces using
drilling and completion fluid system, thereby offering better protection for
low-permeability and extra-low-permeability reservoirs.
When fields are constructed and the top of the reservoir surface closes, 0.3%
water-block resistance agent FCS-08 and 2% acrylate polymer-based oil protec-
tion agent LCM-8 are added to alter the upper drilling fluid in order to
improve the properties of rock surfaces. The drilling completion fluid system
is used and offers protection to low-permeability and extra-low-permeability
reservoirs. Results from testing the properties of rock surfaces are shown in
Table 6.7.
The rheological properties of drilling fluids change slightly before and after
modification, and the compatibility of FCS-08 and LCM-8 with other treat-
ment agents is better. The filtration rate of drilling fluid system and shale
expansion declines after modification, and the cutting recovery and permeabil-
ity recovery values increase greatly. The daily production is 1.6 times that of
adjacent wells, and there is also better protection to low-permeability and
extra-low-permeability reservoirs.
In addition, this system has been promoted and applied in other wells in the
Shengli oilfield. So far, there have been no complications related to drilling
fluids in the wells. Compared to conventional reservoir protection technolo-
gies, the degree of damage to reservoirs decreased significantly. The daily pro-
duction per meter under differential pressure unit increased greatly, when
compared with earlier protection technologies (shown in Table 6.8). There are
remarkable reservoir protection and economic benefits.