This paper deals with a pilot project for the development of a project for the development of a relatively low-transmissibility, tight area of a limestone reservoir in the Khafji Field. In the project, the Productivities of two wells, K-A and K-B. Productivities of two wells, K-A and K-B. were enhanced by acid-fracturing and horizontal drilling. The objectives of this paper are to investigate the effectiveness of the above two methods and to seek the possibility of developing the tight zone.
In K-A, where the acid-fracturing was applied, a laboratory core tent as well as intensive field tests such as a stop rate injection test, pump in/flow back test and mini-fracturing test were performed. Bottom hole pressure measurements and production loggings during such field tests were important in determining accurate fracturing parameters for effective acid-fracturing design. K-B was initially completed as a vertical well with the productivity enhancement by foam-acid fracturing, and was later converted to a horizontal completion well — two horizontal holes were drilled by side-tracking from the existing casing. This paper principally reviews the various well stimulation techniques applied in these two wells such as limited entry, mini-frac optimization, foam acid and gelled acid fracturing and a newly applied horizontal completion technique. The horizontal completion was evaluated in terms of completion technique, stimulation for the horizontal holes and well testing. The two field applications in the project indicated prospective stops for future development prospective stops for future development of the tight zone.
The "A" Limestone Reservoir, which is a symmetrical anticline structure trending NE-SW, was discovered in 1960 in the Khafji Field, offshore Saudi Arabia (Fig. 1) and it started production of 27.4 degrees API [0.890 g/cm3] oil in 1964. 25 wells have been completed for this reservoir (Fig. 2) and the cumulative oil production totalled 70.3 MMSTB [11.2 × 10 m3] as of the and of 1988. The reservoir in the lower part of the Ahmadi Formation of the Middle Cretaceous Wasia Group, and lies in depths from 4100 ft [1250 m] to 4500 ft [1372 m] with an average thickness of 180 ft [55 m]. The reservoir was divided into four layers, Layer 1 to Layer 4 according to the petrophysical features. It has been considered that only Layers 1 and 3 (10–40 ft [3.0–12.2 m] thickness) are productive, and natural fractures have been observed in some wells in these two layers. Layers 2 and 4 are generally low permeability and non-productive zones. Reservoir and geological investigation revealed that the reservoir was of a depletion type without water and gas cap drives. Therefore, in order to maintain pressure, water injection was started in 1976 by spontaneously dumping water from upper aquifers into the reservoir.