The Yamal region of Western Siberia holds enormous reserves of gas and condensate across many geologic layers including the Achimov deposits of the Late Jurassic and Early Cretaceous. The Achimov however, is among the most challenging layers in the Yamal area with deep bedding, very low permeability, thin laminations and abnormally high reservoir pressures that all greatly complicate the appraisal and production of hydrocarbons. In this regard, accurate formation evaluation is essential to ensure efficient and economically reasonable methods of production. Modern methods of openhole logging, including NMR, acoustic and wireline formation testers (WFT) provide advanced information about the formation and can aid in the most efficient development. In this article we present the results of advanced methods of openhole logging that provides greater understanding of the characteristics of the Achimov reservoir. Special NMR measurements were used to estimate the residual fluid saturation which was confirmed with WFT tools designed for downhole fluid analysis and sampling. We also show how to overcome the negative impact of supercharging on measurements of formation pressure in the Achimov formations and the necessity of carrying out such measurements to validate the hydrodynamic reservoir model. To understand the validity of the samples acquired downhole a simulation was carried out further showing the range of possible variations of the basic PVT properties of hydrocarbons during the sampling. The results of advanced acoustic logging allows to estimate the anisotropy of the mechanical properties of the Achimov layers. The use of the data allowed us to model the fractures resulting from hydraulic stimulation and showed significant differences in the geometric characteristics of the fracture between wells and explains why the lower section of the Achimov are often depleted with respect to the upper sections.

Wireline formation testing in open hole can yield robust and reliable information about reservoir fluid type and productivity. However, operational or logistical concerns can sometimes preclude gathering a full open hole formation tester data set. In this case the operator is left to either forgo the information or acquire the data in cased hole. Perforating and production testing in cased hole can be time consuming and expensive especially when there are multiple layers to be tested. This can be mitigated by using wireline formation testers (WFT) in cased hole to test individual layers, but these testers have traditionally been limited in their possible interval length. In this paper we discuss cased hole wireline formation testing with a unique configuration of the WFT that allows testing intervals much greater than previously possible.Wireline formation tester tools with straddle packers are typically limited to about 1-m spacing between the packers. With special adaptors spacings up to 3 m have been accomplished. However, when perforated intervals are longer than this the straddle packer is not an option: it is usually inadvisable to set the elements across perforated casing and cracks in the perforated cement can make the fluid typing ambiguous. This paper discusses a method whereby two separate straddle packer tools are combined and allow a significantly longer interval to be tested.We present a case study where the extended interval was tested and flowed for several days with the formation tester and a confident determination of fluid type performed. Additionally, a long build-up time enabled us to derive a robust estimation of permeability. The operation was concluded in three days versus the ten days of rig time that would have been expected for a cased hole production test. We also show how this method can be extended to longer intervals in both open and cased hole. We conclude that this method is should be considered for zones that could not be tested in open hole but are not worthy of a full production test in cased hole.Although cased whole WFT operations with straddle packers have been reported in the literature this is the first instance of a double WFT tool arrangement that allows testing layers of significant perforated length. Operational guidelines and environmental limitations are also discussed.

In a recent Em-Egovskoe well an extended logging suite was performed with the aim to evaluate the petrophysical properties of Jurassic and Paleozoic formations as well as to improve the structural geological model of this part of the oilfield and to do detailed characterization of the dynamic model by desired properties of formations and fluids. Apart from a standard "triple combo" logging suite the following advanced technologies were applied in the well: neutron-gamma spectroscopy, nuclear magnetic resonance, formation micro imager, formation testers in different modes of reservoir and fluid properties evaluation. Noteworthy, the zone of interest was considered to contain only oil-saturated reservoirs – no gas cap was expected. Indeed on the initial triple combo log data there were no routine gas attributes were observed. Gas-saturated reservoirs were only observed based on integrated analysis of standard and advanced log data, particularly, nuclear magnetic resonance and cross-dipole sonic measurements. Gas-saturated intervals were fully proven by formation tester using downhole fluid analysis (DFA) As a result, one of the Jurassic layers was acknowledged as gas/gas-condensate saturated down to the bottom and the rest of Jurassic intervals were found to be oil saturated. The Abalak formation was also encountered in this well and evaluated. Thin carbonate streaks were identified with the micro-imager and were tested with the dual-packer module of the wireline formation tester. The result was the first ever Abalak oil sample in this field. Furthermore, based on pressure transient analysis of the build-up from the pressure test it was suggested that these tight streaks are laterally discontinuous. Finally, we created a stress profile in the Jurassic and Paleozoic layers. Based on formation micro-imager and acoustic scanning measurements the maximum horizontal stress directions and magnitudes were estimated. Then dual-packer formation tester micro-stress measurements were made to acquire direct measurements of fracture closure pressure. These measurements were used to calibrate our stress model.

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Objectives & Scope The case study presents an application and comparison of different wireline formation testing technology to acquire vital pressure data and downhole fluid samples in tight sub-milidarcy heterogeneous carbonate fields. Examples from Kazakhstan, where tools with different configuration of fluid intake positions and shapes, various flowing areas, are presented to allow us to compare and contrast the performance of each in more complex and challenging reservoir conditions. Methods, Procedures, Process First part of the study discusses the comparison between inflatable straddle packer and radial probe in terms of their data quality and efficiency of the acquisition, where both of the tools were deployed to measure formation pressure, conduct downhole fluid analysis and acquire downhole fluid samples. While the second part focuses on comparison between single probe and radial probe, where both of them were deployed in the well together and were intended to get formation pressure measurements in the zones with the lowest porosity. Results, Observations, Conclusions Extreme downhole conditions pose a challenge to formation testing, acquisition of accurate reservoir pressure data and representative formation samples have proved difficult in cases of highly heterogeneous low porosity and low permeability reservoirs. In the first part of the study, the performance of the each tool compared with different observations such as: average time to first hydrocarbon, average volume to first hydrocarbon, water fraction content, and sampling and downhole fluid analysis by formation zones and by mobility ranges. In the second part, the study elaborates on pressure survey conducted in tight highly heterogeneous carbonate reservoir, where tool with large flowing area and circumferential flow shows its superiority, thus improving operator's reservoir evaluation. Downhole positions of both tools against formation features, such as vugs, porous spots and anhydrite inclusions, were reconstructed on microimager log. Novel/Additive information This case study describes and compares the approaches and methodologies to acquire and perform complex interpretation of critical formation pressure data in heterogeneous carbonate reservoir. The learnings from this successful acquisition and interpretation can substantially improve the reservoir characterization of similar fields worldwide.