Pressure Behavior Analysis of Permeability Changes Due to Sand Production in Offshore Loose Sandstone Reservoirs Using Boundary-Element Method

Abstract

In recent years, sand production has been frequently observed in offshore weakly consolidated sandstone reservoirs. Permeability changes due to sand migration seriously affect the confidence in well test interpretation, production forecasts, and oilfield development plan schedules. The purpose of this paper is to propose a comprehensive model of coupled sand migration, stress sensitivity, and high viscosity oil and to study the effect of sand production induced permeability zoning on transient pressure behavior by combining discrete boundary and discrete wellbore with the boundary element method. In this two-zone composite model, the reservoir can be divided into the inner zone with the improved permeability due to sand migration and the outer zone with initial reservoir permeability. The multifactor effects of stress-sensitive, highly viscous oil, sand migration, and horizontal well are included in this model. Thus, the seepage equation presents a highly nonlinear and difficult to obtain an accurate analytical solution. In this paper, the boundary element method (BEM) is introduced to separate the boundary and wellbore, and the semianalytical solution of the hybrid model is obtained. The comparative analysis of measured pressure curve fitting from a horizontal well, located in the eastern of the South China Sea, proves that this comprehensive model can be used for pressure transient analysis of the weakly consolidated sandstone reservoir. The flow regime analysis indicates that a two-zone composite system may develop seven flow regimes: the wellbore storage stage, early-time radial stage, first transition stage, inner linear stage, inner pseudoradial flow, transition flow from the inner area to the outer area, and outer pseudoradial flow. Sensitivity analysis indicates that the smaller the sand production radius, the shorter the duration of the transition flow from the inner to the outer zone, which suggests the well is mainly affected by the outer boundary in the later period. The larger the permeability ratio, the higher the pressure curves may move up.

Experimental Investigation into Limit Void Ratio Characteristics of Calcareous Sands considering Various Factors

“…(1) The maximum and minimum dry density test should adopt the vibration-hammer method and slow measuring cylinder methods, respectively. To avoid the influence of equipment on experimental results, measuring cylinder and compaction cylinder with a volume of 1000 mL should be used (2) An almost linear relationship exists between the maximum and minimum void ratios of various mixed graded sand. The relationship has a high correlation coefficient of 0.9 and can be used to approximately evaluate e max from e min and vice versa…”

“…Calcareous sands are special soils, which are biogenic sediments and skeletal remains of marine organisms. The main composition is calcium carbonate with a lower hardness than silica sands [1][2][3][4][5][6]. They are widely distributed in shallow, warm, and continental shelf seas.…”

Influence of Sand Production Damage in Unconsolidated Sandstone Reservoirs on Pore Structure Characteristics and Oil Recovery at the Microscopic Scale

“…Unconsolidated sandstone reservoirs have shallow burial depths, poor cementation, large differences in reservoir petrophysical properties, complex pore throat structures, strong heterogeneity, and easy formation of favorable zones for oil and gas production and storage. , However, with the progress of oilfield production operations, the drag force of the reservoir fluid on the rock skeleton particles increases, resulting in obvious sand production in the reservoir. , Sand production in unconsolidated sandstone reservoirs results in lower rock strength. Meanwhile, the permeability is reduced, the microscopic pore throats are blocked by sand particles, and the dominant seepage channel for crude oil is reduced. − Improving single-well productivity under the premise of effective sand control is the key to the development of unconsolidated sandstone reservoirs.…”

Numerical Simulation Investigation on Well Performance Integrated Stress Sensitivity and Sand Production

“…However, few models have been reported considering the synthetical impact of sand migration and stress sensitivity [22][23][24][25]. Reference [26] established a bizonal radial composite model considering the effect of stress sensitivity and sand production. Unfortunately, the well performance is not evaluated under such multiple factors.…”