Abstract: Well Judayaah-1 is an exploration well in Yemen 71 zone. When cementing the third section with ?244.5 mm casing, some difficulties rose as relative high gas reservoir pressure, long cementing section, and high risk of gas cross-flow. To guarantee the cementing quality, the cementing difficulties was analyzed. According to the well condition, it was chosen that the ISO BLOCK slurry system and MUDPUSH weighting spacer from Schlumberger, and H-ES two-stage cementing tool from Halliburton. With the pressure calculation formula for slurry weight loss, the calculation formula was derived for maximum block length above the objective gas formation, and the annular liquid column was designed. To ensure the operation safety and cementing quality, pressure building by cycling friction was taken for the first stage cementing, and pressure building on top head was taken for the second stage cementing. The success of cementing Well Judayaah-1 supplied a reference for the follow-up cementing work in the zone and proved the feasibility of the derived calculation formula for maximum block length above the objective gas formation.