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"Maximising Asset Value and Improving Recovery Factors" in Indian Brown Field Context
Tapas Kumar Sengupta, General Manager - Head Well Services, ONGC Maximising Asset Value and improving recovery factors from Brown fields in the India context is not only desirable but also imperative due to the supply-demand scenario of oil and gas in our country. Revitalising these fields and improving production is an ongoing process and some of the enabling technologies along with their impact are discussed in the article.

Maximising Asset values and improving recovery factors has always been an important aspect of the E&P Business. The demand-supply gap for hydrocarbons in India is huge and is set to widen even further in the future. Although there are opportunities to augment local hydrocarbon production due to vast unexplored basins, improving the recovery factors of reservoirs of brown fields is essential to reduce the impact of the ever widening demand-supply gap.

In the last few years the prices of oil and gas and their derivatives have been spiraling higher. From the mid-1980s to September 2003, the oil price was generally under USD 25/barrel. During 2003, the price rose above USD 30 and peaked at USD 147.30 in July 2008. For a time, geo-political events and natural disasters indirectly related to the global oil market had strong short-term effects on oil prices but by 2008, such pressures appeared to have an insignificant impact on oil prices given the onset of the global recession. The recession caused demand for energy to shrink in late 2008, with oil prices falling from the July 2008 high of USD 147 to a December 2008 low of USD 32. Oil prices stabilised by October 2009 and established a trading range between USD 60 and USD 80. Since January 2011 the price kept on increasing and touched USD 110. Presently it is around USD 105. Like prices of other commodities the price of crude oil experiences wide price swings in times of shortage or oversupply. The crude oil price cycle may extend over several years responding to changes in demand as well as OPEC (Organisation of Petroleum Exporting Countries) and non-OPEC supply.
The primary reason for this has been the inability of supply to cope up with the demand of these products. The new discoveries in the last two decade have been few and far apart. The geo-political scenario especially in the major oil producing countries has been strained and shows no signs of easing up. Meanwhile the growth story in the BRIC countries continues. All this has led to a huge increase in prices. Increasing recoveries from existing fields helps bridge the demand-supply gap to some extent. Higher prices give a boost to R&D and enable companies to deploy newer and more expensive technologies to improve recovery factors in brown fields. The scope to develop already explored marginal fields which were earlier unviable has also got a boost.

The existing fields in India were put on production in the late 70s and early 80s and they have been on production since the last 30 years now. Even after 30 years of production the recovery factors have been in the range of 35 per cent and there remains ample scope of improving these recovery factors to move them closer to the world average of 40-45 per cent. There are some inherent advantages to the redevelopment of brown fields to enhance recovery factors. Since the field has already been on production, most of the infrastructure required to produce incremental oil and gas and to transport it to refining facilities is in place. This greatly enhances the economics of revitalising a brown field. The historical production data and relevant geological and geophysical data are already available. So not only is the cost of acquiring this data avoided, the risk involved in new exploration is also mitigated.

The opportunities for developing the brown fields arise due to low natural energy in some reservoirs, inefficient sweep of secondary recovery techniques, reservoir properties like oil-wet reservoirs and technological evolution. Apart from the above mentioned technical aspects, changing economic scenario and pricing of hydrocarbon products also plays a crucial role in brown field development.
Although revitalising brown fields to enhance recoveries seems to be a lucrative and necessary option, it poses immense challenges in successful implementation. The fields in India are complex in nature. Hence the revitalisation campaign entails fur ther data acquisition, analysis and implementation of the appropriate enabling technologies to extend the life of the mature fields. Some of the technologies that enable mature field revitalisation can be listed as advanced characterisation techniques (e.g., 3D seismic and new measurement, tomographic, and visualisation techniques), reservoir simulation, permanent down-hole reservoir monitoring, horizontal and multilateral drilling, geo-steering, production-enhancement techniques (e.g., secondar y- and ter tiar y-recover y schemes), improved per foration and stimulation methods, new fracturing techniques and fluids, cuttingedge completion technologies, advanced logging techniques, artificial-lift optimisation, and conformance control. It takes the right data, the right tools and techniques, and the right team to create an efficient, cost-effective field-development plan to optimise an aging asset.

Infill drilling, drilling additional wells in the existing well pattern to alter the formation-fluid flow paths and increase sweep to areas where greater hydrocarbon saturations exist is an established optimisation task. This technique is used successfully the world over by most of the E&P companies. In India too, this technique is used to enhance production and improve recovery factors. It not only accelerates recovery but also increases ultimate recovery especially in heterogeneous reservoirs. Using Infill drilling, water flooding efficiency can be improved and bypassed oil can be tapped and produced.

Another popular technique used frequently is drilling multilaterals and horizontal wells. Drilling Multilaterals might lead to immense cost savings when deployed properly. There is an efficient utilisation of slots in offshore and allows tapping of reservoirs at different depths reducing the surface footprint of the wells. They also lead to increase in productivity. Drilling horizontal wells increases the drainage area many folds compared to conventional wells leading to higher production rates. Since the horizontal sections are accurately placed in the oil bearing strata and away from OWC and GOC, they help in reduction of oil and gas coning and delays production of water.

Drilling technology has improved many folds over the years with newer techniques and equipment getting available every day. Rotary steerable systems and down hole motors have not only reduced drilling times but also increased the accuracy of well placements greatly. Measurement while drilling and logging while drilling techniques have further increased well placement accuracies.

Another popular drilling technology is sidetracking the wells with low productivity or wells with depleted saturations. Drain holes are also being done in offshore wells regularly to increase reservoir exposure thus leading to accelerated production. Stimulation techniques may also be used to change wettability of reservoir rock. This may also lead to increased flow rates. During production phase, heterogeneous flow of hydrocarbon fluids and production of fines also leads to increase in skin. To overcome this issue and improve productivity, matrix stimulation is the most preferred and cost effective technique being used. Hydraulic fracturing, as a well stimulation technique is being utilised to increase well productivity and improve recovery factors. Fracturing is carried out to improve productivity by creating fractures. These fractures increase permeability and lead to high flow rates and improve recovery especially in tight formations. Scaling and wax deposition is another issue which leads to fall in productivity of the wells and needs to be managed. This also affects flow assurance. This is generally being tackled using acid pickling, CTU drilling and placement of chemicals to dissolve wax.

The brown fields in India have been producing for an average of 35 years. The reservoir pressures have depleted and are now sub hydrostatic. Water flooding is the preferred reservoir pressure maintenance technique being used. The injection of water also serves the purpose of sweeping oil towards the well bore. This leads to better recoveries and sustaining production rates for a longer duration. Water flooding projects incorporate huge CAPEX& OPEX and hence need to be properly designed and executed to achieve the goals.

Gas lift is another popular artificial lift technique used to lift oil from the well bore to surface in fields where the reservoir pressure has depleted to an extent where it is insufficient to lift the oil to surface. In this technique high pressure gas is used to reduce the density of the reservoir fluid to enable it to lift it to the surface. Aninherent advantage of these systems is their flexible capacity. Addition of a gas lift system to a well where the system is already being used in other wells is very cost effective. The system is also capable of handling a moderate amount of solids and sand which is a distinct advantage over pumps. The system can be effectively deployed in deviated wells also. Some difficulty in implementation is seen in Extended Reach Drilling (ERD) wells where the angle is build up at shallow depths to increase horizontal drift.

Artificial lifting of well fluids from the well bore to surface can also be achieved using pumps. A wide variety of pumps are available like Sucker rod pumps, screw pumps and electrical submersible pumps. In India all of the above are being used depending on their suitability. Electrical submersible pumps are now being used in offshore as they are good for extremely high volume lift and small foot print.

In-situ combustion is being used by ONGC in Balol and Santhal fields; Polymer flooding in Sanand field, Gas Injection in GS-12, Gandhar field and Water injection in Western offshore. Apart from this pilot projects have been started for Alkali-Surfactant-Polymer flood in Viraj and Lakwa fields.

The economic aspects like Oil and gas prices, the future scenario regarding supply and demand, payout times, Return on investment (ROI) and Internal Rate of Return (IRR) are some of the crucial economic aspects of undertaking brown field development.

To achieve the envisaged 40 per cent recovery or more from our oil assets above techniques or their combination is being used depending on the reservoir conditions. Furthermore, efforts have to be made to develop new IOR techniques specific to the Indian sub-continent. With the rising crude prices it is possible that many expensive techniques may soon become feasible to extract the last drop from our depleting reservoirs. Brown field development is of utmost importance due to increasing supply-demand gap. Development of newer, more efficient IOR methods have helped in maximising asset value. On the financial front, increasing prices have led to deployment of techniques which were earlier thought to be uneconomical.

In the Indian context, Maximising Asset values and improving recovery factors is necessary as the large portion of the country’s need is being imported.