Evaluation of IOR Techniques at the Ula Field

Abstract

Copy right 7996 , Stee ri ng Comm ittee of the Euro pean I OR -Symposium . Th is paper was presented at the 8th . Eu ropean I OR -Symposium i n Vienna, Austr i a , May 16 -17 . 1995 Th is paper was setected for presentation by the Stee ring Comm ittee , fol low i ng review of information contai ned in en abstract subm itted by the author(s). The paper, as p resented hes not been reviewed by the Stee ring Committ ee . Abstrac tThe Ula reservoir consists of ons main reservoir unit whic h presently is very we ll swe pt b y injected water, and ons uppe r reservoir uni t from whic h [here i s significantly lower oi l recovery d us to its lower permeability.The paper presents results from a feasibility study which indicates that botte horizontal Wells and WAG injection would increase oil recovery in the upper, low permeable reservoir unit .The WAG potential in the upper unit is highly dependent on a number of parameters, such as the presence of high permeable streaks in the main reservoir unit, the k"/kh ratio in the upper unit and gas relative permeability . The study indicates, however, that although WAG potential from the upper reservoir unit is affected by these parameters, the overall WAG potential remains relatively unchanged . As will be discussed below, changes in critical parameters which significantly reduce the upper unit WAG recovery appears to enhance the main unit recovery .Since the drieling of horizontal Wells located close to the top of the structure affects mainly recovery Erom the upper unit, the potential for this method is more sensitive to changes in upper unit reservoir properties, particularly the k,lkh ratio, but also weel length and location within the upper unit. the end of 1994 was 48 mill . Sm3 o ut of a total rese rve of 69 mill . Sm3.The Ula main reservoir u nit is a fine to me d i um grai ned shal l o w marine sandstone wit ti typi cal pe rmeabi li ty i n th e range 50 m D -500 m D . The uppe r reservoi r uni t is fine grained witti rela t ively low permeability in the range 1 m D --10 mD . The permeabi l ity i n th e upper reservoir un it dec reases up wards .A t present, the Ula Field is operaled by 6 pe r iphera l wate r injectors witti 8 cresta l oil producers . 'ne Bistance betwee n the water injec t ors and the producers is typically in the order of 2 km .Witti the presen t well locations, the water floo d sweep efficiency and recovery is high throughou t the main reservoir uni t . The upper 'uni t, whic h contain s approximately 20 % of the total STOOI P , is howeve r poorly swep t by the curren t water injection scheme.WAG injection is reported to have a significant potential in North Sea reservoirs in generale . Simulation studiesZ and field trials3 indicates that the main WAG target is oil at the top of formation which is not recovered by water flooding . Horizontal Wells are reported to have a potential for increasing oil production rats and reduce coning in thin low permeable reservoir zones, compared to vertical wells4,7 .The paper discussen WAG injection and horizonta l ...