In order to carry out hydrocarbon production in the basement, a drilling must be carried out and the latter crosses several layers or formation until reaching the desired objective. At the beginning of the production, the well will have a natural pressure and the oils in a reasonable quantity which will allow to make an exploitation but over time the pressure decreases and the production of oil leaves room for the production of water to show the end oils and in most cases this well is converted from producing well into an injector well to feed other wells or repackage. In fact, the Tshiende field comprises three reservoirs (Cenomanian, Pinda and Vermelha) that produce and the Cenomanian only produces in its lower horizon. The entire well passes through the Cenomanian reservoir to reach the other two reservoirs. To contribute to the understanding of the geological complexity of the reservoirs of this field, we focused our study on the Cenomanian reservoir. This reservoir did not produce in its superior horizon in the Cenomanian after several tries, but Produces in other fields that the Tshiende field, and that sometimes constitutes the main reservoir in the field Muanda. A new production test in the Ts-27 well began on 02/01/2019 in the Cenomanian dedicated upper part using other technique than the previous ones. This has had to prove the feasibility of producing this unknown reservoir. The decision was made to re-evaluate the UC potential and to propose wells to perforate to depend on their positions and history. After an extensive review of Tshiende's potential for superior Cenomanian production, a development program is proposed. Four workovers are proposed to develop the higher Cenomanian potential in the TS-29, TS-22, TS-02 and TS-13 wells.

The quantity of hydrocarbons initially in place and the technique of exploitation employed in the reservoir determine the period of an oilfield. But the quantity of hydrocarbons in a reservoir defines as a preliminary the type of mechanism drainage which governs the pressure of the oilfield. And this pressure is the key parameter of the oil production. Thus, the mechanism of drainage is a motive element which shows the performance of an oil reservoir during the production. During the oil production in the Upper Pinda reservoir of the Libwa field, the mechanism of drainage used was that of gases in solution. It was noticed that during the production, an abrupt drop of the pressure of 2670 psia with 1567 psia and a cumulated production of oil of 239805 Stb at the end of the year 2018. However, certain studies undertaken in this field revealed the presence of a gas cap which could compensate for the mechanism with dissolved gas but which seemed to be ineffective during the drop pressure. Thus through our study, we put in evidence the existing quantity of gas in the primary gas cap which are worth 1.09414 MMscf under the basic conditions and with the factor of the primary gas cap (m) with 0.0018 who is scarcely and the new gas cap which is created starting from the addition of a quantity of dissolved gas released during the production of which the quantity of this gas is estimated at 1.86329 MMscf under the basic conditions and, the new factor of the gas cap (m) is worth 0.0059 and the value of this new factor of the gas cap (m) is almost null too. Taking into consideration these result, it is shown that this new gas cap will be always ineffective with the performance of the reservoir. On this it is necessary that the factor of the gas cap reaches a value at least equal to 10 to completely replace the mechanism with gas dissolved in the Upper Pinda reservoir in the Libwa field.

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