Vertical Interference tests (VIT) are used to determine the hydraulic connectivity between the formation sand intervals. This paper showcases an innovative workflow of using the petrophysical log attributes to characterize a heterogeneous reservoir sand by making use of ANN (Artificial Neural Net) and SMLP (Stratigraphic Modified Lorentz) based rock typing techniques as well as image based advanced sand layer computation techniques.
Vertical interference test is either performed using a wireline formation testing tool with multiple flow probes deployed in a vertical sequence at desired depth points on the borehole wall or using a drill stem test configuration. Based on the test design, flow rates are changed using downhole pumps, which induces pressure transients in the formation. The measured pressure response is then compared with a numerical model to derive the reservoir parameters such as vertical permeability, hydraulic connectivity etc. The conventional way of model generation is to consider a section of reservoir sand as homogenous, which generally leads to over estimation or underestimation of vertical permeabilities. The technique proposed in this paper utilizes advanced logs such as image logs; magnetic resonance logs, water saturation and other advanced lithology logs to obey heterogeneity in the reservoir model by utilizing ANN/SMLP based rock-typing techniques. These rock types would be helpful in making a multi layer formation model for the VIT modeling and regression approach. The vertical interference test model is then used to determine the vertical permeability values for each of the individual rock types. The paper displays the workflow to utilize the rock type based layered formation model in vertical interference test modeling for a channel sand scenario.
Vertical Interference Tests (VIT) using wireline formation testers are industry standard tests to estimate the vertical permeability of reservoir pay zones. In general, the test interval is considered homogeneous for the interpretation, leading to an inaccurate estimation of vertical permeability (Kv) in complex geological systems like thin laminated beds, channel sands, etc. This paper presents a novel approach of accounting for this heterogeneity through use of petrophysical and borehole image-based rock-typing methods, thus leading to a more realistic characterization of vertical permeability.
Advanced petrophysical logs and images are used to generate rock types through Artificial Neural Network (ANN) and Stratigraphic Modified Lorentz Plot (SMLP) techniques. These rock types are then used as an input into vertical interference test interpretation model, thereby factoring in the reservoir heterogeneity for deriving the vertical permeability. This is followed by a sensitivity analysis to examine the impact of the permeability results in multiple geological systems like channel sands, thin bed lamination, near to fault, pinch outs etc.
Vertical permeability (Kv) is a major input in majority of the advanced reservoir engineering calculations and has a significant impact on the field development plan and IOR/EOR techniques. This unique approach of accounting for rock types in a VIT interpretation model leads to a relatively good estimation of vertical permeability. The rock typing techniques used here, allow the user to define the number of layers and minimum interval thickness, which is extremely useful in highly laminated reservoirs. The sensitivity analysis plays a key role in understanding the utility limitations of both conventional and new approach in complex geological systems. In case of thick homogeneous reservoir, sand units, the conventional approach could be used with fairly accurate results. However, in cases of thin sand-shale units with low net-to-gross ratio, this approach gives a good estimation of layer-wise permeability distribution.
This paper presents a unique blend of petrophysical and dynamic workflows into a novel workflow. The results from the sensitivity study, discussed in the paper, can be used as standard criteria in determining the best suitable technique for interpretation of a vertical interference test. This unique approach allows the user to optimize on the interpretation time and to simultaneously ensure the accuracy of results.
Kumar, Animesh (Indian School of Mines University) | Dutt, Ankit (Indian School of Mines University) | Singh, Suraj (Indian School of Mines University) | Sikarwar, Shailesh Singh (Indian School of Mines University) | Das, Rajarshi (Oil & Natural Gas Corp. Ltd.) | Kumar, K. (Oil & Natural Gas Corp. Ltd.) | Kumar, Kishore
This paper presents the scope of using "Foam Fracturing?? technology in oil wells of India. Since the inception of foam stimulation technique in 1968, it has not been utilized/implemented in India despite of its various unique advantages.
"Foam Fracturing?? was very successful in Arkansas. 8 wells were drilled in the Pettit Limestone formation. Initial production averaged 4.8m3/d, but after 8 weeks, the production started to decline and the wells were stimulated with a 60-65% quality foamed acid. After treatment, the production enhanced to 6.6 to 11.4 m3/d. This paper consist many other examples of success of "Foam Fracturing?? technology in wells of different regions and state.
The unique advantages of foam as frac-fluid are:
1. Exceptional flow-back and clean-up.
2. Reduced liquid volume.
3. Good proppant-carrying capabilities.
4. Less operation time.
The paper also explains the basic properties of foam which makes it economically viable. There is also detailed discussion on the design of foam to suit the candidate well in the best possible way. A comparative study of different oil wells of India which were treated with the conventional frac-fluid to that where foam fracturing was used in different countries was done. The conditions of these wells are very much similar to the wells here in India.
The new fields in India like Krishna-Godavari (KG) basin and Cauvery basin are also suitable for "Foam Fracturing?? technology.
Thus, through the endeavor, we want to conclude that the technology of "Foam Stimulation?? can prove fruitful in India as well and hence must be implemented at the earliest.
N.B.: The laboratory and numerical simulation work for modeling foam as frac-fluid for Indian oil-wells are in progress.
Key words: Foam Fracturing, Prospects in India, foam quality, foam design, KG basin, and flow back capabilities.