Cyclic CO 2 huff 'n' puff process in diverse reservoir conditions, such as immiscible, near-miscible, and miscible, has been tested in the laboratory and applied in the fields as a viable secondary or tertiary means to recover the residual oil in water flooded reservoirs or pressure depleted reservoirs. Recently, petroleum operators have shown increasingly interest in taking CO 2 huff 'n' puff process as a preferred option to extract light oil in low-pressure and low-permeability reservoirs.In this paper, experimental results from a series of coreflood tests are presented and operation strategies for cyclic CO 2 injection are optimized to maximize the light oil recovery factor in a low-permeability reservoir with low original reservoir pressure and while, minimize CO 2 utilization. 6 cyclic coreflood tests, 20 cycles in total, are conducted in a 973 mm-long composite core with an average porosity of 9.6% and an average permeability of 2.3mD. The reservoir pressure is 12.9MPa, far below the measured MMP value of 23MPa, which indicates that the reservoir has no sufficient energy support to do primary production. The impacts of primary operational parameters, such as slug size, injection pressure, chasing gas (N 2 ) and CO 2 injection rate on the performance have been investigated.It is concluded that, on the basis of experimental data, 0.1PV seems to be an optimal slug size for the first cycle, with a cycle recovery factor as high as 14.52% when reservoir pressure depleted to 8MPa. The recovery factor is suggested to be sensitive to the maximum pressure and the maximum pressure should be built up to as high as formation permits. In the following cycles, injecting N 2 as chasing gas after CO 2 injection seems to improve the cycle performance significantly and concurrently reduce the CO 2 utilization. The optimal operation should have three cycles and the ultimate recovery factor for these three cycles could reach above 30%. The findings of this paper extend the understanding of cyclic CO 2 operation and may be employed as technique reference for cyclic CO 2 process operations in low-pressure and low-permeability closed boundary reservoirs.

Paleomagnetism and K–Ar dating of Permian, Triassic, and Cretaceous rocks from Morocco. We have sampled and studied volcanic rocks from the whole of Morocco. Permo-Carboniferous rocks give a magnetic pole situated at 36°N and 238°E (four sites, K = 23, A95 = 20°). Triassic dolerites dated on plagioclases from 205–180 Ma have a mean pole at 72°N, 218°E (34 sites, K = 17, A95 = 6°). Middle Jurassic and Lower Cretaceous basalts and dolentes from l'Atlas de Beni Mellal (ages from 170–120 Ma) have a pole at 45°N and 251°E (13 sites, K = 26, A95 = 8°).The results may be interpreted by clockwise rotation within Morocco. We compare them also with those from other continents.

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CO2 Huff 'N' Puff has been used on a shallow light oil field to add value to existing oil producing wells by increasing the ultimate oil recovery. Testing was initiated in 1985 with a more continuous program starting in 1989. The application of CO2 Huff 'N' Puff has increased oil production 180,000 bbls above the primary recovery with the use of 210 MMCF (12,200 tons). The CO2 treatments have been relatively small with 390 treatments performed on 240 wells. Introduction The Huff 'n' Puff or Cyclic W2 Process is a type of production well stimulation which involves a) injecting CO2 (either as a gas or a liquid) into a well, b) shutting in the well to allow the CO2 to dissipate and dissolve, and c) producing the well back. While each phase of the process is unique, each phase inter-relates mechanically as well as in the reservoir. Field results, reservoir analysis, and computer simulation and matching, indicate that the primary recovery mechanisms in this immiscible CO2 application appear to be 1) a shift in the CO2 saturated water/oil relative permeability, and 2) the forming of a trapped gas saturation, namely within the water phase, which results in a strong decrease of water relative permeability end point. P. 505^

Laboratory and field results are presented for two Rumanian fields: Suplacu de Barcau and Balaria. Insitu combustion is in the industrial stage at Suplacu de Barcau (38 air-injection wells), and the Balaria project (now 5 air-injection wells) is being expanded. Data given include air injected, oil produced, cumulative air/oil ratio, and composition of gas produced. These data, with measurements of temperature and thickness burned, have been used to follow and control the process.

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