The study of gas-condensate reservoirs has been a fruitful field of research in the last years because of their peculiar behaviour. Gas cycling is the recovery process of choice for gas-condensate reservoirs but this process can often not be implemented because of economic reasons. Nitrogen is a potential alternative injection gas. Nevertheless, this has also disadvantages. The application of these processes is more complex in the offshore sites. This paper describes laboratory studies performed to evaluate the effectiveness of some gases (CO2, N2, lean natural gas) in displacing condensate from naturally fractured gas-condensate reservoirs (offshore field). Numerous hurdles had to be overcome. The experiments represented the behavior of a reservoir under HP/HT conditions, 334 °F and 8455 psia. The results of CO2 and natural depletion showed little difference in their ability to recover condensate. The natural gas raised the recovery of the light fraction, but, by contrary, the addition of N2 made evident to be less effective than the rest. The residual saturations and condensate recovery were measured and the results are presented. The detailed analyses revealed that natural gas seems to have been more effective in recovering condensate. Under these conditions, condensate recovery will significantly increase if the lean natural gas is injected. The answers are in agreement with the simulation model. The conclusions are relevant to the overall management of gas-condensate reservoir. These experiments will serve as a guideline to develop the long term corporate strategy to improve additional recoveries in Mexico.

Acidizing and acid fracturing techniques are routinely used in two important formations in the marine regions of Mexico, the Jurassic and Cretaceous formations. These formations are naturally fractured carbonate and dolomite reservoirs having a permeability in the range of 0.19 to 22 mD, porosity from 2.8 to 6%, approximate bottomhole temperature (BHT) up to 177°C, pressure (BHP) of 10,374 psi, and a crude of 45° API. Using acid fracturing techniques helps improve the development of these assets. This paper shows the results of more than 40 acid fracturing operations performed in recent years. Depending on the productivity evaluation, wells belonging to these assets are stimulated as part of the completion stage. Because of their low permeability, a common approach is to perform an acid fracturing operation. As a first evaluation, a minifrac test is executed to obtain the necessary data to calibrate the acid fracturing simulation model. After this step is performed, the acid fracturing design is evaluated. Generally, a sustained production acidizing technique is used for conductivity enhancement and closed-fracture acidizing is also included as a tailored treatment with an all seawater-based acidizing system. For these operations, an average five-fold increase in oil production has been observed after treatment. In some cases wells in the completion stage, having no production before treatment, delivered up to 7000 BOPD after treatment. In these low-permeability assets, the post-fracturing response shows good results in general terms, increasing final conductivity in the near-wellbore area, and improving the production in these wells. The fracture gradient observed varies from 0.715 to 0.981 psi/ft with an average minimum stress of 13,670 psi. To perform the acid fracturing treatments, an average of 6400 hydraulic horsepower (HHP) must be available, with up to 13,400-psi surface pressure observed. As such, a stimulation vessel is necessary in all operations, applying a 26-bbl/min average pumping rate. Globally, acid fracturing treatments are a common stimulation technique. This study shows that stimulating proper candidates in Mexico using acid fracturing significantly helps increase production, which may be relevant for the exploitation of new areas where fracturing has not been implemented.