Research On Cement Slurry Of Controlling Shallow Flow Damages In Deep Water

With the increase of the proportion of offshore oil exploitation, offshore oil exploration is gradually developing into the deep water area to find new petroleum resources, however, all kinds of complicated problems caused by water depth has brought a more serious challenge for deepwater cementing operation, mainly includes: low seafloor temperature,low fracture pressure gradient and shallow flow damages. Shallow flow damages is one of the more difficultr in deepwater cementing.Shallow flow consists of shallow water flow and shallow gas flow, they are trapped in the mud line following150～1100meters, Shallow flow is particularly dangerous for cementing. On the one hand, shallow flow often leads to excessive borehole scour, borehole deformation, difficult hole cleaning, which factors will affect the cementing and lead to poor cementing interface cementation and generation gap. On the other hand, in cement slurry Curing period, high-pressure shallow fluid will gush from weak sedimentary strata, invade the cement slurry, caused fluid channeling, channeling effects produced, cement cementing performance, reducing the cement annulus sealing effect, risks to the cementing operation, even caused a serious shallow flow disaster, endanger the well operation and production safety, so it is necessary to study the technology on cement slurry controlling shallow fluid damages in deep water.Study on cement slurry of controlling shallow fluid damages, developing a set of low temperature and low density cement slurry system which can control of shallow fluid damages in deep water and effectively cement surface, which is the key to ensure the effective development of offshore exploration and development. The main technical difficulty is mainly reflected in the following aspects:1) Because deepwater submarine mud line temperature is very low, the conventional cement low temperature performance can not meet the requirements of low temperature in deep water;2) seabed mud offline stratum failure pressure low and need to have low density slurry matching stratum failure pressure changes;3) mud offline strata high-pressure shallow brine the existence of such fluid, need cement slurry with excellent right-angle thickening and anti-channeling performance, control shallow fluid damages in deep water.In China, the development of cement slurry on control of shallow fluid damages in deep water is a new attempt, through the analysis of causes, harm and control of shallow fluid damages, this paper presents the cement slurry on control of shallow fluid damages in deep water should have the following properties:(1) with a low density of performance, so as to avoid leakage seabed soft stratum;(2) has low filtration, can improve the ring air gas channeling ability.(3) the stable performance, will be zero free water and good sedimentation stability control of formation fluid invasion and channeling, thereby improving the cement bond strength and the sealing effect.(4) with low early strength of cement slurry, the early strength development quickly, can be of sufficient strength to form in a relatively short period of time to reduce the risk of shallow flow damages.(5) has a right angle thickening, thickening transition time is short, the grout can be quickly converted into solid state from liquid state, reducing the probability of occurrence of shallow water flow and air flow, guaranteeing cement after construction can realize hydraulic sealing interlayer isolation;(6) with channeling cement slurry performance, good anti-channeling performance to control shallow flow channeling possibility, deep and shallow flow damages risk reduction.Through selection and evaluation of cement and additives, this paper obtained the cement and cement additive fluid loss additive CG88L, coagulant ACC, retarder H21L, domestic Floating Bead and stabilizer STAB, which are suitable for cement slurry on control of shallow fluid damages in deep water. And through the test, this paper determined the additive dosage and constructed a set of cement slurry system on control of shallow fluid damages in deep water.1.30g/cm3slurry formulation:blend cement+75%seawater+0.2%Defoamer CX66L+4%Fluid Loss Additive CG88L+1.5%coagulant ACC+0.5%retarder H21L+35%domestic Floating Bead+1%stabilizer STAB;1.40g/cm3slurry formulation:blend cement+65%seawater+0.2%Defoamer CX66L+4%Fluid Loss Additive CG88L+1.5%coagulant ACC+0.5%retarder H21L+31%domestic Floating Bead+1%stabilizer STAB;1.50g/cm3slurry formulation:blend cement+58%seawater+0.2%Defoamer CX66L+4%Fluid Loss Additive CG88L+1.5%coagulant ACC+0.5%retarder H21L+20%domestic Floating Bead+1%stabilizer STAB;1.60g/cm3slurry formulation:blend cement+53%seawater+0.2%Defoamer CX66L+4%Fluid Loss Additive CG88L+1.5%coagulant ACC+0.5%retarder H21L+12%domestic Floating Bead+1%stabilizer STAB;1.70g/cm3slurry formulation:blend cement+50%seawater+0.2%Defoamer CX66L+4%Fluid Loss Additive CG88L+1.5%coagulant ACC+0.5%retarder H21L+7%domestic Floating Bead+1%stabilizer STAB;1.80g/cm3slurry formulation:blend cement+48%seawater+0.2%Defoamer CX66L+4%Fluid Loss Additive CG88L+1.5%coagulant ACC+0.5%retarder H21L+1%stabilizer STAB.This paper evaluates the comprehensive performance of cement slurry system on control of shallow flow damages in deep water, and evaluated the temperature sensitivity, stress sensitivity, coagulant and retarder dosage sensitivity, low temperature strength, low temperature filtration, low temperature stability, contamination resistance, low temperature thickening and thickening transition time and anti-channeling performance and other aspects of the evaluation. The results showed that the cement slurry system with adjustable thickening time (120-300min), the density and water loss control, the rapid development strength at low temperature, high early strength (10℃/24hr strength can reach5MPa), thickening transition time is short (less than 10min). Through the use of cement channeling coefficient method to calculate the cement slurry SPN value between0.62-1.85, which fully shows that cement slurry have good anti-channeling performance and have good effect in the control of shallow flow damages in deep water.