For thin oil rim reservoir with gas cap and edge water, it is
helpful to improve the development effect to find out the distribution law of
remaining oil in this kind of reservoirs. For this reason, taking the narrow
oil rim reservoir with gas cap and edge water of Oilfield A in Bohai Sea as a
case, the main controlling factors, including reservoir structure, fault, gas
cap energy, edge water energy and well pattern, affecting the distribution of
residual oil in this kind of reservoir were analyzed by using the data of core,
logging, paleogeomorphology and production.
Then, the distribution law of remaining oil was summarized. Generally, the
remaining oil distribution is mainly potato-shaped or strip-shaped in
plane. Vertically, it depends on the energy of gas cap and edge water. For the
reservoir with big gas gap and weak edge water, the remaining oil mainly lies
in the bottom of oil column. And for the reservoir with small gas gap and
strong edge water, the remaining oil mainly locates at the top of oil column.
Aiming at different distribution modes of remaining oil, the corresponding potential
tapping strategies of horizontal wells are put forward: in the late stage of
development, for the reservoir with big gas gap and weak edge water, the remaining
oil concentrates at the bottom of the oil column, and the position of
horizontal well should be placed at the lower 1/3 to the lower 1/5 of the oil
column; for the reservoir with small gas cap and strong edge water, the remaining
oil locates at the top of the oil column, and the position of horizontal well
should be put at the upper 1/5 to the upper 1/3 of the oil column height,
vertically. Based on the study on remaining oil of Oilfield A, a potential tapping
strategy of well pattern thickening and vertical position optimization of
horizontal well was proposed. This strategy guided the efficient implementation
of the comprehensive adjustment plan of the oilfield. Moreover, 18 infill
development wells were implemented in Oilfield A, and the average production of
the infill wells is 2.1 times that of the surrounding old wells. It is
estimated that the ultimate recovery factor of the oilfield will reach 33.9%,
which is 2.3% higher than that before infilling wells. This study can be used
for reference in the development of similar reservoirs.