A Method for Calculating Oil Field Relative Permeability Curve by Using Water Drive Characteristic Curve in High Water Cut Stage

With the production of strong bottom water reservoir, it will soon enter the ultra-high water cut stage. After entering the ultra-high water cut period, the main means of stable production is liquid extraction. Large liquid volume has a certain impact on the physical property distribution and fluid seepage law of the oilfield. The relative permeability curve measured according to the industry standard is not used for the prediction of development indicators and the understanding of the dynamic law of the oilfield. In order to understand the characteristics of water drive law in high water cut stage of water drive oilfield, starting from the water drive characteristic curve in high water cut stage, the method for calculating the relative permeability curve is deduced. Through numerical simulation verification and fitting the actual production data, it is confirmed that the obtained relative permeability curve is in line with the reality of the oilfield, It can provide some guiding significance for understanding the production law and water drive law of strong bottom water reservoir in ultra-high water cut stage.

Harvest Time and Fertility Effects on Yield and Quality of Forage from Alfalfa, Hybrid Bromegrass and Their Mixture

A field experiment with 24 treatments consisting of three perennial forage crops [alfalfa (Medicago sativa L. cv. AC Longview), hybrid bromegrass (Bromus riparius Rehm & Bromus inermis Leyss. cv. AC Success) and their mixture], four Cut 1 dates (approximately June 20, July 10, July 30 or August 20), and two fertilizer levels (unfertilized and fertilized) was established in late May 2014, on a Black Chernozem [Udic Boroll] silty clay soil. Forage dry matter yield [DMY], and concentration (g·kg−1 DM) of crude protein [CP], total digestible nutrients [TDN] and acid detergent fiber [ADF] data were collected over 3 years from 2015 to 2017. The fertilizer treatments were imposed in 2016 and 2017. Forage crops were initially cut at four Cut 1 dates, and again cut [Cut 2] in autumn (September 2 in 2015, November 7 in 2016 and October 5 in 2017). For all three forage crops, forage DMY usually increased when Cut 1 was delayed. Delaying Cut 1 reduced forage DMY for Cut 2. Total DMY (Cut 1 + Cut 2) for all three forage crops was highest from the combination of July 10 and late Autumn cuts. Alfalfa-bromegrass mixture produced higher DMY than bromegrass or alfalfa alone. Fertilizer application resulted in a significant increase in Cut 1 and total DMY for bromegrass. The CP concentration in Cut 1 forage usually declined as the forage crops matured. The CP concentration was highest for alfalfa, followed by alfalfa-bromegrass mixture, and much lower for bromegrass. There was little or no effect of forage crop maturity on the TDN and ADF concentrations in forage. The TDN concentration was higher and ADF concentration was lower in forage from alfalfa or alfalfa-bromegrass mixture than bromegrass. Fertilizer application significantly increased CP concentration for alfalfa-bromegrass mixture. Delaying harvesting for Cut 1 increased ADF yield and TDN yield until Late July, but CP yield generally decreased with crop maturity. The ADF yield and TDN yield were higher for alfalfa-bromegrass mixture than bromegrass or alfalfa alone, and CP yield was similar for alfalfa and alfalfa-bromegrass mixture but considerably higher than bromegrass. Fertilizer application increased CP yield and ADF yield for bromegrass and alfalfa-bromegrass mixture, and TDN yield only for bromegrass. In conclusion, total DMY (Cut 1 + Cut 2) was highest for a combination of Early July and Autumn cuts. Forage yield was highest for alfalfa-bromegrass mixture, followed by alfalfa and lowest for bromegrass. The CP and TDN concentrations were higher, and ADF concentrations were lower in forage from alfalfa or alfalfa-bromegrass mixture than bromegrass.

An effective method to predict oil recovery in high water cut stage

The water flooding characteristic curve method based on the traditional regression equation between the oil and water phase permeability ratio and the water saturation is inappropriate to predict the oil recovery in the high water cut stage. Hence, a new water flooding characteristic curve equation adapted to the high water cut stage is proposed to predict the oil recovery. The water drive phase permeability experiments show that the curve of the oil and water phase permeability ratio vs. the water saturation, in the semi-logarithmic coordinates, has a significantly lower bend after entering the high water cut stage, so the water flooding characteristic curve method based on the traditional regression equation between the oil and water phase permeability ratio and the water saturation is inappropriate to predict the oil recovery in the high water cut stage; therefore, a new water flooding characteristic curve equation based on a better relationship between ln（kro/k,.~） and S~ is urgently desirable to be established to effectively and reliably predict the oil recovery of a water drive reservoir adapted to a high water cut stage. In this paper, by carrying out the water drive phase permeability experiments, a new mathematical model between the oil and water phase permeability ratio and the water saturation is established, with the regression analysis method and an integration of the established model, the water flooding characteristic curve equation adapted to a high water cut stage is obtained. Using the new water flooding characteristic curve to predict the oil recovery of the GD3-block of the SL oilfield and the J09-block of the DG oil field in China, results with high predicted accuracy are obtained.

Micro-distribution and mechanical characteristics analysis of remaining oil

As the water drive reservoir enters extra high water cut stage(greater than 80%),remaining oil distribution becomes increasingly dispersed.Research on micro residual oil in pore appears particularly important for reservoir development at extra high water cut stage.Oil occurrence characteristics recognition helps to understand the distribution of remaining oil and the mechanical characteristics of oil is the guide for tapping the remaining oil.On the basis of pore scale oil ewater two phase flow experiments,micro distribution of remaining oil is divided into four occurrence states in accordance with oil features at different stage of water flooding,the flake of remaining oil,oil column,oil droplet and oil film.A quantitative characterization method of remaining oil occurrence states is established.By using micro numerical simulation method,change rules of four occurrence states of remaining oil during the process of water displacement and the mechanical characteristics of different occurrence state of remaining oil are analyzed.Results show that the continuous oil phase gradually transforms to discontinuous phase and even to dispersed phases during the water flooding process.At extra high water cut stage,most of remaining oil are dispersed oil columns,oil droplets and oil films,which are the main target of remaining oil to be tapped.By changing water flow direction or increasing the displacement pressure gradient,the surface adsorption force acting on oil columns are overcome,and then the oil columns begin to move and finally to be produced out.Oil droplets in pore-throat center are scoured and carried out by water as the increase of the injection volume,while the oil droplets in blind ends and the oil films are extracted out by adding chemicals to reduce the interfacial tension,so as to enhance oil recovery.For water flooding reservoir,the corresponding tapping measures for four types of oil occurrence states brought forward have great meanings of improving reservoir recovery at high water cut stage.