In Asia Pacific region, there are many thinly bedded reservoirs which are composed of interbedded porous and permeable sands with variable proportions of thin silt and clay beds. These reservoir sand bodies range from millimeters to tens of meters in thickness. Though the reservoirs are highly permeable, reservoir heterogeneity caused by silt and clay laminations affect recovery and sweep efficiency. The typical way to test such formations is to use full scale well testing, even for relatively thin zones. In the Gulf of Thailand (GoT), a Tubing Stem Test (TST) is widely used to test each individual zone for reservoir parameters. During a TST, quartz gauges are run on wireline and the selected zone is perforated. While wireline Formation Testers (FT) have also been increasingly used in the GoT for measuring formation pressure, mobility and collecting reservoir fluids, more advanced FT tools, e.g. dual packers and Downhole Fluid Analyzers (DFA) were recently introduced to test each zone to help defining reservoir characteristics in more detail. A single probe FT deployed for pretests and fluid sampling can be used to obtain transient data during the shut-in periods after sampling in relatively thin zones. The data from these Interval Pressure Transient Tests (IPTTs) can be used to interpret reservoir parameters such as vertical to horizontal permeability ratio and horizontal permeability. This paper discusses the uses of such smaller scale pressure transient data (single probe, dual packer formation testers) and full scale well testing using a simulation model and actual field data from the GoT. First, a single well simulation model is used to investigate the effects of thinly bedded shales at different scales on pressure transient data. The actual field data were then analyzed to obtain reservoir parameters and compared with core and PVT lab results. This paper also investigates the use of deconvolution applied to pressure transient tests of different scales to understand the effect of reservoir parameters using simulated and field data. Introduction Thinly Bedded Reservoirs in the Gulf of Thailand In the Tertiary Basins of the Gulf of Thailand and Northern Malay Basin, thinly bedded hydrocarbon sandstone reservoirs have been encountered in several geological settings. In the northern Gulf of Thailand, Kra Basin, subaqueous lacustrine fan delta sandstones of between 1 to 4 feet have developed as a result of episodic deposition. In the Southern part of the Pattani Basin adjacent to the Narathiwat High, thinly bedded reservoirs of less than 1 to 7 ft were deposited in marginal marine, tidally influence estuarine channel fills settings and also in more proximal fluvial crevasse splay deposits.

Pressure transient analysis has been known as an important tool to properly characterize a reservoir. The scales of measurement for different testing methods depend mainly on their radius of investigation, i.e. how far pressure changes/disturbance can be seen into reservoirs. In a large reservoir, a full scale testing method such as a Drill Stem Test (DST) is required to test enough reservoir volume for flow assurance purposes. To test for the reservoir extent, a production test is required to reach reservoir boundaries.In recent years, there have been tremendous developments for short period testing methods. The Formation Tester (FT) is one of the tools that are used to evaluate reservoir fluid properties and acquire pressure transient data from both dual packer and single probe configurations. With the current Downhole Fluid Analyzer (DFA) technology, reservoir fluid properties such as composition, Gas-Oil-Ratio (GOR), in-situ density, and viscosity can be obtained in real time. These insitu fluid properties can be used to analyze pressure transient data for reservoir permeability, skin factor, and reservoir heterogeneity; and as a result, the DFA serve to push IPTT applications to another step forward. This paper will specifically focus on the application of DFA for IPTT purposes and also a continuation of several published papers which discussed the use of different scales of pressure transient data. The results from this paper will mainly focus on the use of single probe and dual packer IPTT to obtain reservoir properties in thinly bedded reservoirs with waxy crudes from the South East Asia region. The viscosity variation from oil based mud filtrate to reservoir fluid during the pump-out and its effect on the pressure derivative will be discussed using actual examples to demonstrate this point.The end results may contradict traditional testing methods on the use of virgin reservoir fluid properties for pressure transient analysis. Hopefully, this paper might open another option when FT is deployed together with the current DFA tool for quick and effective reservoir evaluation in thinly bedded reservoirs which are often encountered in many parts of the world. TX 75083-3836, U.S.A., fax +1-972-952-9435

Thin beds are a prominent feature in many recently discovered hydrocarbon reservoirs around the world. Not only are they typically difficult to evaluate, which leads to high reserves uncertainty, they are also frequently associated with inconsistent well performance. One of the main challenges in the evaluation of thinly-bedded reservoirs is an accurate productivity assessment. High-resolution borehole image logs provide us with detailed information on the internal structure of reservoirs sands, sand quality indications as well as a net-to-gross determination. Reliable formation evaluation requires further high-resolution petrophysical and geophysical logs (for an initial permeability estimation, free fluid volume, saturation, formation anisotropy and structural information). However, as per reservoir testing information (pressure, fluid types, PVT properties, permeability and producibility), this dynamic reservoir characterization method needs to be properly planned and evaluated. In the past, the use of full scale Drill Stem Test and Production Tests were conducted to obtain reservoir parameters including zone productivity. However, due to costly operations especially in marginal and also deepwater reservoirs, different scales of pressure transient test have been introduced1, 2, and 3. Several publications have discussed the use of smaller scale testing to obtain reservoir information. However, there have been no publications showing a complete comparison of pressure transient data obtained from several scales of measurement when heterogeneity is present in the reservoirs. This paper therefore aims to present a comparison of results obtained from alternative formation testing methods in a relatively thin (ten of meters) formation which are a single probe Wireline Formation Tester, dual packer Wireline Formation Tester, and full scale well test. This paper also discusses ways to optimise the testing methodology in such thin reservoirs. The application of an Interval Pressure Transient Test (IPTT) using a single probe as well as the dual packer WFT are illustrated and discussed in details. Their applications, specifications, advantages and disadvantages over the conventional testing method are extensively covered. This study aims to aid in devising suitable field development strategies at an acceptable cost while maintaining satisfactory operational efficiency.