Laminated units made up of alternating thin sand and mud layers are known to be very challenging in terms of reservoir characterization and evaluation. Alternation of thin sand and mud layers imposes natural anisotropy in the distribution of reservoir properties such as porosity and permeability. This anisotropy has been proved to be a major control on fluid flow within the reservoir which is of paramount importance to understand and consider in reservoir development planning. The aim of this work is to integrate geological information derived from borehole images into interval pressure transient test (IPTT) interpretation to analyze and explain the complex flow behavior resulting from a combination of formation dip and laminations.A wireline formation tester dual packer module was utilized in two offshore exploration wells to conduct an IPTT/miniDST (mini Drill Stem Test) in different lithofacies including laminated units. Several build up tests were performed to obtain valid reservoir pressure and permeability values. Consistency was observed in the log-log diagnostic plot from these build up tests and the pressure derivative behavior suggests multiple possible reservoir scenarios in this complicated geological setting. A detailed study on borehole images and 3D near-wellbore geological model revealed the effects of slanted wellbore, laminated units and dipping beds on the travel of pressure transient away from wellbore. With this information, a representative reservoir model was able to be constructed to match the IPTT data and to obtain the required reservoir parameters.This paper highlights the main challenges of formation characterization in laminated thin sand and mud layers. Special emphasis was given to resolve significant problems encountered in pressure transient test interpretation in highly deviated wells. Slanted wellbore sections are typical in Malaysia's offshore fields as the wells are drilled from offshore platform to intercept the formation at different angles, hence the pay zone and other petrophysical parameters are usually underestimated. Attempts are made to identify and classify these challenges, and recommendations are provided toward better resolution during interpretation.

Cendor Graben Shallow sands are 35 Km2 of gas accumulation at depth varying from 350-450mss over the Jambu-Liang anticline, defined by high amplitude in seismic, containing hydrocarbon gas (C1-C3gas indicated by mudlogs) with the possibility of high CO2; possibly charged from deeper sources though fault seeps. Shallow Gas reservoirs also due to the unconsolidated formation present unique measurement and operations challenges to the wireline formation tester (WFT) in pretesting and sampling due to its nature of high compressibility especially at low pressure. Often the high gas compressibility results in a larger pretest drawdown volume needed to decompress the flowline and to reduce the flowline pressure below the formation pressure for a valid formation pressure measurement. The good mobility formation further complicates the flowline decompression due to a very small pressure drawdown. In addition, at the start of pretest build-up period, a pressure build-down behavior was observed and has greatly affected the formation pressure stabilization and mobility calculation. On the other hand, gas sampling in such low pressure and unconsolidated formation introduces great difficulties in balancing the samples bottle filling and sand production initiation which may potentially plugged the downhole pump-out module. The station time limitation commonly imposed by the drillers making the sampling process even more challenging. In the past, companies often considered these sands as drilling hazards and not targets for exploitation. This testing validated the importance of formation testing in shallow unconsolidated gas reservoirs by preventing formation failure that could lead to plugging. The small sand particle sizes and unconsolidated nature of the formation makes it very difficult to control sand production. This work presents an exploration work done in a very shallow and low pressure gas bearing formation, which exposes the WFT to a combination of unconsolidated formation and high gas compressibility challenges. Best practices are established and discussed in this paper to address the aforementioned challenges to enable a successful WFT evaluation in the shallow, low pressure gas reservoirs.