Rock wettability is one of the most important factors driving oil recovery mechanisms, as it controls the location, flow and distribution of reservoir fluids. Wettability affects most of the petrophysical properties of reservoir rocks including capillary pressure, relative permeability, waterflood behavior, electrical properties, and enhanced oil recovery (EOR). Most reservoir rocks are water-wet since they were originally formed in marine or lacustrine sedimentary environments. During hydrocarbons migration, reservoir rocks can be reversed to oil-wet conditions because of surface electrical charges of the grains that attract the oppositely charged components contained in the migrating hydrocarbon phase. Carbonatic reservoir rocks normally show a moderate to strong oil-wet condition. Alkaline substances and some surfactants have the capability to reverse the oil-wet reservoir rocks into a more favorable condition for enhancing oil production. In particular, such mechanism is normally deployed to increase the oil recovery factor of chemical flooding EOR projects. Laboratory testing at reservoir conditions is
always required before implementing any field application and the wettability reversal measurement is a key factor for the success of the above EOR application. The present study was performed at the Petroleum Engineering laboratory of the University of Bologna (Italy). Here, it has been clarified that the displacement-by-oil ratio significantly affects the Amott-Harvey wettability index, which affects the final oil recovery expected by the application of alkali and alkali-surfactant
flooding EOR technique. On the other hand, only a small change of displacement-by-water ratio can be observed throughout the experiments. This observation can be interpreted as the improvement of oil recovery factor induced by alkali and alkalisurfactant flooding is caused primarily by a lesser preference to oil more than by the complete reversal of previously oil-wet into full water-wet condition. In particular, the maximum relative oil recovery of the strong oil-wet carbonatic rock is obtained when the Amott-Harvey wettability index is close to zero or when the reservoir rock turns into a neutral-wet condition.
Yuzhi, Xue (Drilling Technology Research Institute) | Gongrang, Li (Drilling Technology Research Institute) | Baofeng, Liu (Drilling Technology Research Institute) | Zhang, Jinghui (Drilling Technology Research Institute)
The Well Shengke-1 is one of ultra-deep wells with total depth of 7026m, bottom hole temperature of 235 ? and more than pressure of 100MPa. Ultra-deep well drilling fluid faces many serious challenges. Severe engineering problems would arise if the drilling fluid is not treated properly and even the success of the well is determined by the drilling fluid. The difficulties including complex formation, long barefoot borehole, and ultra-high temperature were confronted. The stratums of f215.9mm hole included section KongDian 1 and section KongDian 2, in which the clay minerals in upper shale stratum consist of mainly mixed layer of inordinate illite and montmorillonite. Therefore, the troublesome conditions could probably occur during drilling. The open-hole interval was as long as about 3000m, and pressure indices of formations varied enormously. In upper stratum, after high pressure brine formation had been drilled at 4598m, the density of drilling fluid increased to 1.83g/cm3. Meanwhile, the pressure index of under-stratum was about 1.30g/cm3, so lost circulations had happened many times in high differential pressure. The high temperature of the drilling would induce complicated reaction between the clay and drilling fluid so as to slough of the clay. During drilling yield point and gel strength increased quickly with the effect of high temperature. The Poly-sulfonate plugging and anti-sloughing (5155~4598m), high density poly-sulfonate non-invasive (4598~5800m), and ultra-high temperature and super high density drilling fluid( 5800~7026m) had been used in 215.9 mm interval of the well, respectively. The drilling fluid kept stationary for a long time during completion which caused drilling fluid thickening, dehydration and mud cake thickening. The solid-free anti-high temperature completion fluid was used to guarantee the success of logging and casing. It was proved in the field application of Shengke1 that the drilling fluids exhibited a series of advantages, including excellent rheology behavior, good thermal stability and low filtration rate. It was easy to treat, formulate and maintain, and could deal with the salt and brine contamination. It had been stable under 235? of the BHT in Shengke1, the highest temperature encountered in China at that time, and guaranteed the well to be completed successfully.
Catastrophic losses accompanied by reservoir fluid influx that are commonly experienced when drilling oil and gas wells through fractured and vugular carbonates in Indonesia were solved using a managed pressure drilling (MPD) variant called pressurized mud cap drilling (PMCD) to drill through the loss zones and reach target depth (TD) with minimal non-productive time. The well is closed in on a rotating control device (RCD) and a light annular fluid column or mud cap is maintained in the annulus, while sacrificial drilling fluid, mostly water, is pumped through the drillpipe and together with the cuttings, are swept into the loss zones. The method has been largely successful in allowing adopters to reach TD, but difficulties as to how the liner and well completion can be run in PMCD mode have been encountered. The requirements of completing the well in PMCD mode most of the time leads to countless failed attempts to kill the well or circulate a mud weight that is at balance with formation pressure.
Recent PMCD operations, however, have provided success stories as to liner and well completion running, both in the onshore and offshore setting in Indonesia. These successes have largely been brought about by appropriate liner / completion system design and by the adoption of new techniques that complement the procedures involved in operating in PMCD mode. These methods have allowed for the proper management of pressures while running liner / completion with total losses and have subsequently allowed the containment of the same. The details of these methods employed for running liners and well completion safely, efficiently and successfully in PMCD mode in onshore and offshore locations in Indonesia are provided in this paper, as well its capabilities and limitations. The set-up of the liner and completion equipment that have been run in PMCD mode along with recommendations for improvement are also discussed.
The empirical range of deliverability ratio between horizontal well and vertical well is usually regarded as 2-5. But actually, this range is too large and the real ratio may not be within it. To quantify the deliverability ratio relationship between horizontal well and vertical well more accurate, the deliverability ratio relationship is derived based on modified Joshi's horizontal well deliverability formula and vertical well deliverability formula. Then as for different horizontal well lengths with known parameters of the pay zone in the vertical well where the horizontal well locates, corresponding deliverability ratios can be obtained. And then the horizontal well deliverability can be predicted by multiplying the known appraisal well (vertical well) deliverability and the deliverability ratio.
Sensitivity analysis between the deliverability ratio and relevant parameters is done by using pay zone, fluid and well parameters of Q oilfield of China Bohai Bay. The results show that as for different parameter combinations, the deliverability ratio can be within or without the range of 2-5; skin factor and off-center distance have little effect on the deliverability ratio, while as horizontal length increases, permeability anisotropy factor increases and pay thickness increases as well as drainage radius decreases, the deliverability ratio will decrease obviously. These regularities coincide with actual development regularity, which verifies the accuracy of the proposed method.
The proposed method quantifies the deliverability ratio range between horizontal well and vertical well, and increases prediction accuracy of horizontal well deliverability; therefore it is of great practicability, especially for early stage reservoir development.
The mountainous high steep structure in Tarim Basin, as a result of orogenesis, owes presses solid, structure extrusion factor and so on, caused the geology conditions, which the drilling operation must cope with, are very complex: The reservoir buried so deeply (the maximum depth presented 7600m), And there developed an very thick evaporate bed as coverage in Tertiary, which buried from 1526m to 7070m. So the formation pressure coefficient to reach to as high as 2.47, the density of drilling fluid used during operation reached as high as 2.55 sg the most, and BHT exhibited 186? (Tests on site). Another problem is that there
exhibited extensive interconnected fractures in the reservoir, which caused the serious loss circulation and overflow occurred frequently during drilling. Faced so many extreme formidable drilling conditions, This paper identifies and discusses the major HP/HT/HS drilling fluid challenges, the ultra high-density water-based drilling fluid designs, the key laboratory studies about the fluid`s properties, and other considerations in HP/HT drilling.
Up to now, about 23 ultra-deep wells (>6000m) and 3 ultra-deep wells (>7000m) have been completed in Tarim, which are achieved by the application of a series of advanced techniques, especially the High-performance drilling fluids, which are briefly described in this paper, especially the results and observations are presented in YS-1(total depth is 7258m), DB-3(total depth is 7090m) and KS-2(total depth is 6780m) wells. Finally the paper identified some of the drilling fluid challenges that still lie ahead during the ultra-deep drilling process.
Yanayacu Oilfield in Block 1AB/8 belongs to strong natural water driving oilfield with over 30 years development history in Peru rainfall region. The comprehensive water cut is 95% by 2005. This paper reviews a multidiscipline comprehensive study on potential tapping in this oilfield. Based on re-explained reservoir structure and secondary logging interpretation, as well as comprehensive geological study, fine reservoir 3D model was built and residual oil distribution was characterized. Reservoir simulation is conducted and result shows well pattern is the dominant controlling factor of residual oil. The well spacing is about 750-1000m, and there is no well drilled in structural high part in the north region, which leads to relatively enriched residual oil potential in the structural high part. The residual oil distribution is also affected by interlayer and barrier. According to residual oil distribution result, horizontal wells were deployed in relatively structural high part to tap residual oil, and re-perforation, layer transformation and bridge plug were applied in high water cut wells with interior barrier and interlayer. According to adjustment plan, two horizontal wells and one directional well were drilled in 2006, where the initial production of two horizontal wells is over 3300bbl/d, which is over 5 times of the highest initial production of previously drilled wells in this field. The comprehensive water cut of this field is dropped from 95% to 89.5% by the end of 2008.
Block 8 and 1-AB are situated in south America rainforest jungle region in Peru, which is approximately 700 kilometers from Pacific Coast(Fig.1). Block 8 and 1-AB were discovered in 1971, and put into production since 1974. The reservoir belongs to Upper Crataceous formation. The reservoir buried depth ranges from 2200 to 3700m. The peak production reached 140,586 BOPD in 1979. CNPC bought 45% share of Block 1-AB and 27% share of Block 8 from Pluspetrol company in 2003, and Pluspetrol are operator of the block.
Yanayacu oilfield is one of the 19 oilfields in Block 8 and 1-AB. Yanayacu oilfield belongs to strong water drive reservoir .The reservoir pressure only drops about 240psi after 30 years production. The strong bottom water not only provides driving energy for oil production, it also arouses strong water coning which decrease displacement efficiency and oil recovery ratio.
The obduction zone of Kunlun mountain foreland in southwest Tarim basin in China is covered with thick loess whose thickness changes from several decade meters to 500m, even up to 600m in some area, so, the S/N of seismic data acquired in this area is very low due to serious absorption and attenuation of seismic wave and develops strong secondary interference. Being extruded and compressed by Kunlun Mountains, the topography of this area changes rapidly, the subsurface structure is steep and complex, and the faults are very developed, which lead this area to be one of the most difficult areas to do seismic exploration in the world. The conventional seismic exploration techniques used previously can't meet the requirements of the oil/gas exploration any more, and in the area since 1978, after the Kekeya oilfield was discovered, there has been no breakthrough made. Since 1999, several seismic technique tackling studies on
Kekeya edge have been carried out, and wide line receiving and source array with deep holes have been applied, but the effects are not good. In recent years, on the basis of the previous rounds of seismic exploration tackling results in the thick loess area, new research has been conducted, and seismic data with relatively high S/N been acquired, which can meet the requirements for geological interpretation. Moreover, aimed at this thick loess area, seismic acquisition
technique series have been developed, and great breakthroughs have been obtained for seismic exploration in loess area, and the first-grade rate of the seismic data increased by about 20%, all of which made a solid foundation for seismic exploration of loess area in southwest Tarim, and these technique series have some reference values for seismic exploration in the similar areas.
The paper introduces some new technical achievements and knowledge for seismic acquisition in loess area of southwest Tarim basin, mainly including: (1) wide-line survey technique with high fold and long receiving spread is applied to increase the effective fold on the target horizons, and improve the quality of the seismic section; (2) source array technique with long pattern length and small charge size is applied to enhance the downgoing energy of the seismic wave; (3) long array receiving technique is applied to suppress the lateral interference and improve the signal sensitivity.
Key words:loess area, seismic acquisition, wide line survey, source array, long array receiving
The obduction zone of Kunlun mountain foreland in southwest Tarim basin in China is covered with thick loess which thickness changes from several decade meters to 500m, even up to 600m in some area, so, the seismic data acquired in this area has very low S/N character due to serious absorption and attenuation of seismic wave and develops strong secondary interference. Being extrusion and compression by Kunlun Mountains, the topography of this area changes rapidly, the subsurface structure is steep and complex, and the faults are very developed. It is one of the most difficult areas to do seismic exploration in the world.
This paper presents a new Flexible Bottomhole Assembly (BHA), which is classified as a coupled driven drilling BHA of the power anti-deviation, with the technical superiority of anti-deviation and high ROP. The coupled driven drilling has simultaneously two driving powers: one is from kelly/rotary-table or top-drive; another is from positive downhole motor (PDM). Comparing with the traditional BHA, the new BHA for coupled driven drilling uses a short flexible sub and the appropriate PDC bits with high hydraulic efficiency and high cleaning and cooling capacity, which has rationally distributed the stabilizers' spacing, and has scientifically designed the structure of PDM centralizer's size.
The new BHA used for coupled driven drilling is based on an integrated mechanical model. Through the analysis on the kelly/rotary-table and rotor centrifugal force and their transmission efficiency, the fulcrum role to PDM centralizer and its leverage ratio, the formation force and the geometric anti-deviation force, and the coupling analysis on the above factors, this paper has set up an anti-deviation force's calculation model of the coupled driven drilling, a relationship model between the allowable well-deviation and the critical WOB, a PDC bit gauge length design model, and the structural designed model of PDM centralizer. According to the above integrated model from the view of the whole system, a set of software moduli, a coupled driven drilling BHA mechanical analysis and drilling parameters optimization, is developed to determine the optimum BHA through different formation parameters, drilling parameters, the design requirements to well-deviation and ROP. The new BHA and the matching technology have been in successful application in the part of oil blocks of the Bohai Sea in China, the ROP and well-deviation meet the design requirements, and borehole quality has been improved significantly.
The concentrations of heavy metals in the soil at oil and gas production areas were appraised at Ebocha and Akri communities in Niger Delta region of Nigeria. The pollution/contamination loading indexes of Zinc (Zn), Nickel (Ni), Copper (Cu), and Lead (Pb) in the two communities were determined from soil samples collected in eight locations (in triplicate) in each community using Atomic Absorption Spectrophotometer (AAS).
It was observed that Ebocha was slightly polluted with lead (contamination/pollution index, c/p = 1.3), severely contaminated with zinc (c/p = 0.642) and slightly contaminated with copper(c/p = 0.123). Omoku was also slightly contaminated with zinc (c/p = 0.225) while all other sampling locations at Ebocha were very slightly contaminated with zinc, copper nickel and lead (c/p <0.1). Akri was very slightly contaminated in all the sampling locations except for Afia-afor where lead slightly contaminated the soil (c/p = 0.113).
A significant correlation (p <0.01) was obtained for zinc (r = 0.65) while there was no significant correlation (0.05 <p <0.01) obtained for Ni (r = -0.14), Cu (r = 0.22), Pb (r = -0.08), Mn (r = 0.38) and Fe (r = 0.54). This correlation showed that the sources of the heavy metals in both communities are different. It was also observed that the increased concentration of heavy metals in oil and gas production areas is more due to other associated human activities in the areas than oil and gas core production activities.
Estimation of the drilling rate of penetration (ROP) has always been a challenge for drilling engineers, since it is the key parameter in drilling optimization. There are many parameters which have significant influence on ROP. Relating penetration rate to these parameters result in defining a model for penetration rate. Hence, several rate of penetration models have been proposed. Among these models, the most well-known ones are Bourgoyne and Young, and Warren's models. In each of these models different parameters have been used to estimate the ROP.
The application of different parameters and their corresponding weights causes the models to predict the ROP with different accuracies. In addition, usage of different assumptions in developing the models results in quiet different areas of application for the two mentioned models. Hence, studying the models' applications and comparison of them would lead to the more successful model recognition.
In this paper, ROP equations are obtained for some depth intervals based on the two mentioned models. For this purpose, drilling data from two wells in one of the Iranian gas fields in Persian Gulf area is used. Based on the resulted equations, the two models are compared and the more suitable equation for future drillings in the same field is proposed.
The result of this study would leads to a large amount of saving in time and money in drilling the new wells. Although one of the models may excel the other one in some cases, it is not true in general. Therefore, some useful recommendations on the usage and application areas of each model will be worked out which leads to low cost drilling, real-time monitoring and optimization, and ROP enhancement.
In the recent years, drilling optimization techniques have been used to reduce drilling operation costs. This would be done by reducing the operation time, since time is always money in drilling operations. The concept of time taking for any drilling operation can be stated in terms of drilling rate of penetration. Therefore, estimation of penetration rate is one of the essential parts of the drilling optimization. To estimate penetration rate, a drilling model has to be developed.
A drilling model is usually a mathematical relationship which relates rate of penetration to the parameters affecting it significantly. There is no exact mathematical relation between drilling rate and different drilling variables because not only a large number of uncertain drilling variables influence drilling rate, but also their relationship is nonlinear and complex (Ricardo et al., 2007). Penetration rate is affected by many parameters such as bit hydraulics, weight on bit, rotary speed, bit type, mud properties, formation characteristics, etc. (Akgun, 2007). During the past years, several drilling models have been proposed for rate of penetration.
In this paper, we first review the background literature on several rate of penetration models. Then, the two more sophisticated models will be analyzed. The estimated rates of penetration by these two models would be compared and recommendations on the application of the two models will be given. Finally, a new model based on the neural networks is developed using neural network fitting tool of the MATLAB programming software. Implication of this model to our data showed the proficiency of the model in comparison to the other models.